diff --git a/Billable.php b/Billable.php
index 15353cb..6a0771a 100644
--- a/Billable.php
+++ b/Billable.php
@@ -7,6 +7,7 @@
 use InvalidArgumentException;
 use Stripe\Charge;
 use Stripe\Customer;
+use Stripe\Error\Card;
 use Stripe\Error\InvalidRequest;
 use Stripe\Invoice as StripeInvoice;
 use Stripe\InvoiceItem as StripeInvoiceItem;
@@ -37,11 +38,11 @@ trait Billable
      * @param int $amount
      * @param array $options
      *
-     * @return \Stripe\Charge
+     * @return Charge
      *
-     * @throws \Stripe\Error\Card
+     * @throws Card
      */
-    public function charge($amount, array $options = [])
+    public function charge($amount, array $options = []): Charge
     {
         $options = array_merge([
             'currency' => $this->preferredCurrency(),
@@ -49,8 +50,8 @@ public function charge($amount, array $options = [])
 
         $options['amount'] = $amount;
 
-        if (!array_key_exists('source', $options) && $this->stripeId) {
-            $options['customer'] = $this->stripeId;
+        if (!array_key_exists('source', $options) && $this->stripe_id) {
+            $options['customer'] = $this->stripe_id;
         }
 
         if (!array_key_exists('source', $options) && !array_key_exists('customer', $options)) {
@@ -68,7 +69,7 @@ public function charge($amount, array $options = [])
      *
      * @return StripeRefund
      */
-    public function refund($charge, array $options = [])
+    public function refund($charge, array $options = []): StripeRefund
     {
         $options['charge'] = $charge;
 
@@ -80,9 +81,9 @@ public function refund($charge, array $options = [])
      *
      * @return bool
      */
-    public function hasCardOnFile()
+    public function hasCardOnFile(): bool
     {
-        return (bool)$this->cardBrand;
+        return (bool) $this->card_brand;
     }
 
     /**
@@ -92,18 +93,18 @@ public function hasCardOnFile()
      * @param int $amount
      * @param array $options
      *
-     * @return bool
+     * @return bool|StripeInvoice
      *
-     * @throws \Stripe\Error\Card
+     * @throws Card
      */
     public function invoiceFor($description, $amount, array $options = [])
     {
-        if (!$this->stripeId) {
+        if (!$this->stripe_id) {
             throw new InvalidArgumentException('User is not a customer. See the createAsStripeCustomer method.');
         }
 
         $options = array_merge([
-            'customer' => $this->stripeId,
+            'customer' => $this->stripe_id,
             'amount' => $amount,
             'currency' => $this->preferredCurrency(),
             'description' => $description,
@@ -124,7 +125,7 @@ public function invoiceFor($description, $amount, array $options = [])
      *
      * @return SubscriptionBuilder
      */
-    public function newSubscription($subscription, $plan)
+    public function newSubscription(string $subscription, string $plan): SubscriptionBuilder
     {
         return new SubscriptionBuilder($this, $subscription, $plan);
     }
@@ -137,7 +138,7 @@ public function newSubscription($subscription, $plan)
      *
      * @return bool
      */
-    public function onTrial($subscription = 'default', $plan = null)
+    public function onTrial(string $subscription = 'default', ?string $plan = null): bool
     {
         if (func_num_args() === 0 && $this->onGenericTrial()) {
             return true;
@@ -148,7 +149,7 @@ public function onTrial($subscription = 'default', $plan = null)
         }
 
         return $subscription && $subscription->onTrial() &&
-        $subscription->stripePlan === $plan;
+            $subscription->stripePlan === $plan;
     }
 
     /**
@@ -156,9 +157,9 @@ public function onTrial($subscription = 'default', $plan = null)
      *
      * @return bool
      */
-    public function onGenericTrial()
+    public function onGenericTrial(): bool
     {
-        return $this->trialEndAt && Carbon::now()->lt(Carbon::createFromFormat('Y-m-d H:i:s', $this->trialEndAt));
+        return $this->trial_ends_at && Carbon::now()->lt(Carbon::createFromFormat('Y-m-d H:i:s', $this->trial_ends_at));
     }
 
     /**
@@ -169,18 +170,20 @@ public function onGenericTrial()
      *
      * @return bool
      */
-    public function subscribed($subscription = 'default', $plan = null)
+    public function subscribed(string $subscription = 'default', ?string $plan = null): bool
     {
         $subscription = $this->subscription($subscription);
+
         if (is_null($subscription)) {
             return false;
         }
+
         if (is_null($plan)) {
             return $subscription->valid();
         }
 
         return $subscription->valid() &&
-        $subscription->stripePlan === $plan;
+            $subscription->stripe_plan === $plan;
     }
 
     /**
@@ -190,7 +193,7 @@ public function subscribed($subscription = 'default', $plan = null)
      *
      * @return SubscriptionModel|null
      */
-    public function subscription($subscription = 'default')
+    public function subscription(string $subscription = 'default'): ?SubscriptionModel
     {
         return $this->getSubscriptions()->where(['name' => $subscription])->one();
     }
@@ -200,19 +203,19 @@ public function subscription($subscription = 'default')
      */
     public function getSubscriptions()
     {
-        return $this->hasMany(SubscriptionModel::className(), ['userId' => 'id'])->orderBy(['createdAt' => SORT_DESC]);
+        return $this->hasMany(SubscriptionModel::class, ['user_id' => 'id'])->orderBy(['created_at' => SORT_DESC]);
     }
 
     /**
      * Invoice the billable entity outside of regular billing cycle.
      *
-     * @return bool
+     * @return bool|StripeInvoice
      */
     public function invoice()
     {
-        if ($this->stripeId) {
+        if ($this->stripe_id) {
             try {
-                return StripeInvoice::create(['customer' => $this->stripeId], $this->getStripeKey())->pay();
+                return StripeInvoice::create(['customer' => $this->stripe_id], $this->getStripeKey())->pay();
             } catch (InvalidRequest $e) {
                 return false;
             }
@@ -226,11 +229,11 @@ public function invoice()
      *
      * @return Invoice|null
      */
-    public function upcomingInvoice()
+    public function upcomingInvoice(): ?Invoice
     {
         try {
             $stripeInvoice = StripeInvoice::upcoming(
-                ['customer' => $this->stripeId], ['api_key' => $this->getStripeKey()]
+                ['customer' => $this->stripe_id], ['api_key' => $this->getStripeKey()]
             );
 
             return new Invoice($this, $stripeInvoice);
@@ -245,7 +248,7 @@ public function upcomingInvoice()
      *
      * @return Invoice|null
      */
-    public function findInvoice($id)
+    public function findInvoice(string $id): Invoice
     {
         try {
             return new Invoice($this, StripeInvoice::retrieve($id, $this->getStripeKey()));
@@ -262,7 +265,7 @@ public function findInvoice($id)
      *
      * @throws NotFoundHttpException
      */
-    public function findInvoiceOrFail($id)
+    public function findInvoiceOrFail(string $id)
     {
         $invoice = $this->findInvoice($id);
 
@@ -281,7 +284,7 @@ public function findInvoiceOrFail($id)
      *
      * @return Response
      */
-    public function downloadInvoice($id, array $data)
+    public function downloadInvoice(string $id, array $data)
     {
         return $this->findInvoiceOrFail($id)->download($data);
     }
@@ -294,7 +297,7 @@ public function downloadInvoice($id, array $data)
      *
      * @return array
      */
-    public function invoices($includePending = false, $parameters = [])
+    public function invoices(bool $includePending = false, array $parameters = []): array
     {
         $invoices = [];
 
@@ -323,7 +326,7 @@ public function invoices($includePending = false, $parameters = [])
      *
      * @return array
      */
-    public function invoicesIncludingPending(array $parameters = [])
+    public function invoicesIncludingPending(array $parameters = []): array
     {
         return $this->invoices(true, $parameters);
     }
@@ -333,7 +336,7 @@ public function invoicesIncludingPending(array $parameters = [])
      *
      * @param string $token
      */
-    public function updateCard($token)
+    public function updateCard(string $token): void
     {
         $customer = $this->asStripeCustomer();
         $token = Token::retrieve($token, ['api_key' => $this->getStripeKey()]);
@@ -376,8 +379,8 @@ public function updateCardFromStripe()
         if ($defaultCard) {
             $this->fillCardDetails($defaultCard)->save();
         } else {
-            $this->cardBrand = null;
-            $this->cardLastFour = null;
+            $this->card_brand = null;
+            $this->card_last_four = null;
             $this->update(false);
         }
 
@@ -394,8 +397,8 @@ public function updateCardFromStripe()
     protected function fillCardDetails($card)
     {
         if ($card) {
-            $this->cardBrand = $card->brand;
-            $this->cardLastFour = $card->last4;
+            $this->card_brand = $card->brand;
+            $this->card_last_four = $card->last4;
         }
 
         return $this;
@@ -423,7 +426,7 @@ public function applyCoupon($coupon)
      *
      * @return bool
      */
-    public function subscribedToPlan($plans, $subscription = 'default')
+    public function subscribedToPlan($plans, $subscription = 'default'): bool
     {
         $subscription = $this->subscription($subscription);
 
@@ -431,8 +434,8 @@ public function subscribedToPlan($plans, $subscription = 'default')
             return false;
         }
 
-        foreach ((array)$plans as $plan) {
-            if ($subscription->stripePlan === $plan) {
+        foreach ((array) $plans as $plan) {
+            if ($subscription->stripe_plan === $plan) {
                 return true;
             }
         }
@@ -447,9 +450,9 @@ public function subscribedToPlan($plans, $subscription = 'default')
      *
      * @return bool
      */
-    public function onPlan($plan)
+    public function onPlan($plan): bool
     {
-        $plan = $this->getSubscriptions()->where(['stripePlan' => $plan])->one();
+        $plan = $this->getSubscriptions()->where(['stripe_plan' => $plan])->one();
 
         return !is_null($plan) && $plan->valid();
     }
@@ -459,9 +462,9 @@ public function onPlan($plan)
      *
      * @return bool
      */
-    public function hasStripeId()
+    public function hasStripeId(): bool
     {
-        return !is_null($this->stripeId);
+        return !is_null($this->stripe_id);
     }
 
     /**
@@ -472,7 +475,7 @@ public function hasStripeId()
      *
      * @return Customer
      */
-    public function createAsStripeCustomer($token, array $options = [])
+    public function createAsStripeCustomer(string $token, array $options = []): Customer
     {
         $options = array_key_exists('email', $options)
             ? $options : array_merge($options, ['email' => $this->email]);
@@ -482,7 +485,7 @@ public function createAsStripeCustomer($token, array $options = [])
         // and allow us to retrieve users from Stripe later when we need to work.
         $customer = Customer::create($options, $this->getStripeKey());
 
-        $this->stripeId = $customer->id;
+        $this->stripe_id = $customer->id;
 
         $this->save();
 
@@ -499,11 +502,11 @@ public function createAsStripeCustomer($token, array $options = [])
     /**
      * Get the Stripe customer for the user.
      *
-     * @return \Stripe\Customer
+     * @return Customer
      */
-    public function asStripeCustomer()
+    public function asStripeCustomer(): Customer
     {
-        return Customer::retrieve($this->stripeId, $this->getStripeKey());
+        return Customer::retrieve($this->stripe_id, $this->getStripeKey());
     }
 
     /**
@@ -511,7 +514,7 @@ public function asStripeCustomer()
      *
      * @return string
      */
-    public function preferredCurrency()
+    public function preferredCurrency(): string
     {
         return Cashier::usesCurrency();
     }
@@ -521,7 +524,7 @@ public function preferredCurrency()
      *
      * @return int
      */
-    public function taxPercentage()
+    public function taxPercentage(): int
     {
         return 0;
     }
@@ -531,7 +534,7 @@ public function taxPercentage()
      *
      * @return string
      */
-    public static function getStripeKey()
+    public static function getStripeKey(): string
     {
         return static::$stripeKey ?: Yii::$app->params['stripe']['apiKey'];
     }
@@ -539,9 +542,9 @@ public static function getStripeKey()
     /**
      * Set the Stripe API key.
      *
-     * @param  string $key
+     * @param string $key
      */
-    public static function setStripeKey($key)
+    public static function setStripeKey($key): void
     {
         static::$stripeKey = $key;
     }
diff --git a/Cashier.php b/Cashier.php
index 805a411..20b3f36 100644
--- a/Cashier.php
+++ b/Cashier.php
@@ -38,8 +38,10 @@ class Cashier
      *
      * @param string $currency
      * @param string|null $symbol
+     *
+     * @throws Exception
      */
-    public static function useCurrency($currency, $symbol = null)
+    public static function useCurrency(string $currency, ?string $symbol = null): void
     {
         static::$currency = $currency;
         static::useCurrencySymbol($symbol ?: static::guessCurrencySymbol($currency));
@@ -54,7 +56,7 @@ public static function useCurrency($currency, $symbol = null)
      *
      * @throws Exception
      */
-    protected static function guessCurrencySymbol($currency)
+    protected static function guessCurrencySymbol(string $currency): string
     {
         switch (strtolower($currency)) {
             case 'usd':
@@ -75,7 +77,7 @@ protected static function guessCurrencySymbol($currency)
      *
      * @return string
      */
-    public static function usesCurrency()
+    public static function usesCurrency(): string
     {
         return static::$currency;
     }
@@ -85,7 +87,7 @@ public static function usesCurrency()
      *
      * @param string $symbol
      */
-    public static function useCurrencySymbol($symbol)
+    public static function useCurrencySymbol(string $symbol): void
     {
         static::$currencySymbol = $symbol;
     }
@@ -95,7 +97,7 @@ public static function useCurrencySymbol($symbol)
      *
      * @return string
      */
-    public static function usesCurrencySymbol()
+    public static function usesCurrencySymbol(): string
     {
         return static::$currencySymbol;
     }
@@ -105,7 +107,7 @@ public static function usesCurrencySymbol()
      *
      * @param callable $callback
      */
-    public static function formatCurrencyUsing(callable $callback)
+    public static function formatCurrencyUsing(callable $callback): void
     {
         static::$formatCurrencyUsing = $callback;
     }
@@ -117,7 +119,7 @@ public static function formatCurrencyUsing(callable $callback)
      *
      * @return string
      */
-    public static function formatAmount($amount)
+    public static function formatAmount(int $amount): string
     {
         if (static::$formatCurrencyUsing) {
             return call_user_func(static::$formatCurrencyUsing, $amount);
diff --git a/README.md b/README.md
index 459671a..6df8ebf 100644
--- a/README.md
+++ b/README.md
@@ -46,23 +46,23 @@ if ($this->db->driverName === 'mysql') {
     $tableOptions = 'CHARACTER SET utf8 COLLATE utf8_unicode_ci ENGINE=InnoDB';
 }
 
-$this->createTable('subscription', [
+$this->createTable('subscriptions', [
     'id' => $this->primaryKey(),
-    'userId' => $this->integer()->notNull(),
+    'user_id' => $this->integer()->notNull(),
     'name' => $this->string()->notNull(),
-    'stripeId' => $this->string()->notNull(),
-    'stripePlan' => $this->string()->notNull(),
+    'stripe_id' => $this->string()->notNull(),
+    'stripe_plan' => $this->string()->notNull(),
     'quantity' => $this->integer()->notNull(),
-    'trialEndAt' => $this->timestamp()->null(),
-    'endAt' => $this->timestamp()->null(),
-    'createdAt' => $this->timestamp()->null(),
-    'updatedAt' => $this->timestamp()->null()
+    'trial_ends_at' => $this->timestamp()->null(),
+    'ends_at' => $this->timestamp()->null(),
+    'created_at' => $this->timestamp()->null(),
+    'updated_at' => $this->timestamp()->null()
 ], $tableOptions);
 
-$this->addColumn('user', 'stripeId', $this->string());
-$this->addColumn('user', 'cardBrand', $this->string());
-$this->addColumn('user', 'cardLastFour', $this->string());
-$this->addColumn('user', 'trialEndAt', $this->timestamp()->null());
+$this->addColumn('users', 'stripe_id', $this->string());
+$this->addColumn('users', 'card_brand', $this->string());
+$this->addColumn('users', 'card_last_four', $this->string());
+$this->addColumn('users', 'trial_ends_at', $this->timestamp()->null());
 ```
 > Also you can apply migration by the following command:
 
@@ -307,7 +307,7 @@ If you would like to offer trial periods without collecting the user's payment m
 ```php
 $user = new User([
     // Populate other user properties...
-    'trialEndAt' => Carbon::now()->addDays(10),
+    'trial_ends_at' => Carbon::now()->addDays(10),
 ]);
 ```
 
diff --git a/SubscriptionBuilder.php b/SubscriptionBuilder.php
index 3eb7749..a8bfe3d 100644
--- a/SubscriptionBuilder.php
+++ b/SubscriptionBuilder.php
@@ -183,13 +183,13 @@ public function create($token = null, array $options = [])
             $trialEndsAt = $this->trialDays ? Carbon::now()->addDays($this->trialDays) : null;
         }
         $subscriptionModel = new SubscriptionModel([
-            'userId' => $this->user->id,
+            'user_id' => $this->user->id,
             'name' => $this->name,
-            'stripeId' => $subscription->id,
-            'stripePlan' => $this->plan,
+            'stripe_id' => $subscription->id,
+            'stripe_plan' => $this->plan,
             'quantity' => $this->quantity,
-            'trialEndAt' => $trialEndsAt,
-            'endAt' => null,
+            'trial_ends_at' => $trialEndsAt,
+            'ends_at' => null,
         ]);
         if ($subscriptionModel->save()) {
             return $subscriptionModel;
@@ -208,7 +208,7 @@ public function create($token = null, array $options = [])
      */
     protected function getStripeCustomer($token = null, array $options = [])
     {
-        if (!$this->user->stripeId) {
+        if (!$this->user->stripe_id) {
             $customer = $this->user->createAsStripeCustomer(
                 $token, array_merge($options, array_filter(['coupon' => $this->coupon]))
             );
diff --git a/composer.json b/composer.json
index f9e108f..a31d9ce 100644
--- a/composer.json
+++ b/composer.json
@@ -15,6 +15,7 @@
         }
     ],
     "require": {
+        "php": ">=7.1",
         "yiisoft/yii2": "~2.0.14",
         "yii2mod/yii2-behaviors": "*",
         "stripe/stripe-php": "~4.0",
diff --git a/controllers/WebhookController.php b/controllers/WebhookController.php
index d9291a7..6338694 100644
--- a/controllers/WebhookController.php
+++ b/controllers/WebhookController.php
@@ -30,7 +30,7 @@ public function behaviors()
     {
         return [
             'verbs' => [
-                'class' => VerbFilter::className(),
+                'class' => VerbFilter::class,
                 'actions' => [
                     'handle-webhook' => ['post'],
                 ],
@@ -46,15 +46,18 @@ public function behaviors()
     public function actionHandleWebhook()
     {
         $payload = json_decode(Yii::$app->request->getRawBody(), true);
+
         if (!$this->eventExistsOnStripe($payload['id'])) {
             return;
         }
+
         $method = 'handle' . Inflector::camelize(str_replace('.', '_', $payload['type']));
+
         if (method_exists($this, $method)) {
             return $this->{$method}($payload);
-        } else {
-            return $this->missingMethod();
         }
+
+        return $this->missingMethod();
     }
 
     /**
@@ -71,7 +74,7 @@ protected function handleCustomerSubscriptionDeleted(array $payload)
             $subscriptions = $user->getSubscriptions()->all();
             /* @var $subscription SubscriptionModel */
             foreach ($subscriptions as $subscription) {
-                if ($subscription->stripeId === $payload['data']['object']['id']) {
+                if ($subscription->stripe_id === $payload['data']['object']['id']) {
                     $subscription->markAsCancelled();
                 }
             }
@@ -94,7 +97,7 @@ protected function getUserByStripeId($stripeId)
     {
         $model = Yii::$app->user->identityClass;
 
-        return $model::findOne(['stripeId' => $stripeId]);
+        return $model::findOne(['stripe_id' => $stripeId]);
     }
 
     /**
diff --git a/migrations/m180321_213759_rename_subscription_table.php b/migrations/m180321_213759_rename_subscription_table.php
new file mode 100644
index 0000000..06af0b5
--- /dev/null
+++ b/migrations/m180321_213759_rename_subscription_table.php
@@ -0,0 +1,25 @@
+<?php
+
+use yii\db\Migration;
+
+/**
+ * Class m180321_213759_rename_subscription_table
+ */
+class m180321_213759_rename_subscription_table extends Migration
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function safeUp()
+    {
+        $this->renameTable('subscription', 'subscriptions');
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function safeDown()
+    {
+        $this->renameTable('subscriptions', 'subscription');
+    }
+}
diff --git a/migrations/m180321_213856_rename_subscription_columns.php b/migrations/m180321_213856_rename_subscription_columns.php
new file mode 100644
index 0000000..93c3f3a
--- /dev/null
+++ b/migrations/m180321_213856_rename_subscription_columns.php
@@ -0,0 +1,51 @@
+<?php
+
+use yii\db\Migration;
+
+/**
+ * Class m180321_213856_rename_subscription_columns
+ */
+class m180321_213856_rename_subscription_columns extends Migration
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function safeUp()
+    {
+        $this->renameColumn('subscriptions', 'userId', 'user_id');
+        $this->renameColumn('subscriptions', 'stripeId', 'stripe_id');
+        $this->renameColumn('subscriptions', 'stripePlan', 'stripe_plan');
+        $this->renameColumn('subscriptions', 'trialEndAt', 'trial_ends_at');
+        $this->renameColumn('subscriptions', 'endAt', 'ends_at');
+        $this->renameColumn('subscriptions', 'createdAt', 'created_at');
+        $this->renameColumn('subscriptions', 'updatedAt', 'updated_at');
+
+        if (Yii::$app->db->schema->getTableSchema('user')) {
+            $this->renameColumn('user', 'stripeId', 'stripe_id');
+            $this->renameColumn('user', 'cardBrand', 'card_brand');
+            $this->renameColumn('user', 'cardLastFour', 'card_last_four');
+            $this->renameColumn('user', 'trialEndAt', 'trial_ends_at');
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function safeDown()
+    {
+        $this->renameColumn('subscriptions', 'user_id', 'userId');
+        $this->renameColumn('subscriptions', 'stripe_id', 'stripeId');
+        $this->renameColumn('subscriptions', 'stripe_plan', 'stripePlan');
+        $this->renameColumn('subscriptions', 'trial_ends_at', 'trialEndAt');
+        $this->renameColumn('subscriptions', 'ends_at', 'endAt');
+        $this->renameColumn('subscriptions', 'created_at', 'createdAt');
+        $this->renameColumn('subscriptions', 'updated_at', 'updatedAt');
+
+        if (Yii::$app->db->schema->getTableSchema('user')) {
+            $this->renameColumn('user', 'stripe_id', 'stripeId');
+            $this->renameColumn('user', 'card_brand', 'cardBrand');
+            $this->renameColumn('user', 'card_last_four', 'cardLastFour');
+            $this->renameColumn('user', 'trial_ends_at', 'trialEndAt');
+        }
+    }
+}
diff --git a/models/SubscriptionModel.php b/models/SubscriptionModel.php
index 837deb5..b46ca2e 100644
--- a/models/SubscriptionModel.php
+++ b/models/SubscriptionModel.php
@@ -7,22 +7,21 @@
 use LogicException;
 use Yii;
 use yii\db\ActiveRecord;
-use yii\db\Expression;
 use yii2mod\behaviors\CarbonBehavior;
 
 /**
- * This is the model class for table "Subscription".
+ * This is the model class for table "subscriptions".
  *
  * @property int $id
- * @property int $userId
+ * @property int $user_id
  * @property string $name
- * @property string $stripeId
- * @property string $stripePlan
+ * @property string $stripe_id
+ * @property string $stripe_plan
  * @property int $quantity
- * @property Carbon $trialEndAt
- * @property Carbon $endAt
- * @property int $createdAt
- * @property int $updatedAt
+ * @property Carbon $trial_ends_at
+ * @property Carbon $ends_at
+ * @property int $created_at
+ * @property int $updated_at
  * @property \yii\db\ActiveRecord $user
  */
 class SubscriptionModel extends ActiveRecord
@@ -44,77 +43,73 @@ class SubscriptionModel extends ActiveRecord
     /**
      * @inheritdoc
      */
-    public static function tableName()
+    public static function tableName(): string
     {
-        return 'subscription';
+        return 'subscriptions';
     }
 
     /**
      * @inheritdoc
      */
-    public function rules()
+    public function rules(): array
     {
         return [
-            [['userId', 'name', 'stripeId', 'stripePlan', 'quantity'], 'required'],
-            [['userId', 'quantity'], 'integer'],
-            [['trialEndAt', 'endAt'], 'safe'],
-            [['name', 'stripeId', 'stripePlan'], 'string', 'max' => 255],
+            [['user_id', 'name', 'stripe_id', 'stripe_plan', 'quantity'], 'required'],
+            [['user_id', 'quantity'], 'integer'],
+            [['trial_ends_at', 'ends_at'], 'safe'],
+            [['name', 'stripe_id', 'stripe_plan'], 'string', 'max' => 255],
         ];
     }
 
     /**
      * @inheritdoc
      */
-    public function attributeLabels()
+    public function attributeLabels(): array
     {
         return [
             'id' => Yii::t('app', 'ID'),
-            'userId' => Yii::t('app', 'User ID'),
+            'user_id' => Yii::t('app', 'User ID'),
             'name' => Yii::t('app', 'Name'),
-            'stripeId' => Yii::t('app', 'Stripe ID'),
-            'stripePlan' => Yii::t('app', 'Stripe Plan'),
+            'stripe_id' => Yii::t('app', 'Stripe ID'),
+            'stripe_plan' => Yii::t('app', 'Stripe Plan'),
             'quantity' => Yii::t('app', 'Quantity'),
-            'trialEndAt' => Yii::t('app', 'Trial End At'),
-            'endAt' => Yii::t('app', 'End At'),
-            'createdAt' => Yii::t('app', 'Created At'),
-            'updatedAt' => Yii::t('app', 'Updated At'),
+            'trial_ends_at' => Yii::t('app', 'Trial End At'),
+            'ends_at' => Yii::t('app', 'End At'),
+            'created_at' => Yii::t('app', 'Created At'),
+            'updated_at' => Yii::t('app', 'Updated At'),
         ];
     }
 
     /**
      * @inheritdoc
      */
-    public function behaviors()
+    public function behaviors(): array
     {
         return [
             'timestamp' => [
                 'class' => 'yii\behaviors\TimestampBehavior',
-                'createdAtAttribute' => 'createdAt',
-                'updatedAtAttribute' => 'updatedAt',
+                'createdAtAttribute' => 'created_at',
+                'updatedAtAttribute' => 'updated_at',
                 'value' => function () {
-                    $currentDateExpression = Yii::$app->db->getDriverName() === 'sqlite' ? "DATETIME('now')" : 'NOW()';
-
-                    return new Expression($currentDateExpression);
+                    return Carbon::now()->toDateTimeString();
                 },
             ],
             'carbon' => [
-                'class' => CarbonBehavior::className(),
+                'class' => CarbonBehavior::class,
                 'attributes' => [
-                    'trialEndAt',
-                    'endAt',
+                    'trial_ends_at',
+                    'ends_at',
                 ],
             ],
         ];
     }
 
     /**
-     * User relation
-     *
      * @return \yii\db\ActiveQuery
      */
     public function getUser()
     {
-        return $this->hasOne(Yii::$app->user->identityClass, ['id' => 'userId']);
+        return $this->hasOne(Yii::$app->user->identityClass, ['id' => 'user_id']);
     }
 
     /**
@@ -122,7 +117,7 @@ public function getUser()
      *
      * @return bool
      */
-    public function valid()
+    public function valid(): bool
     {
         return $this->active() || $this->onTrial() || $this->onGracePeriod();
     }
@@ -132,9 +127,9 @@ public function valid()
      *
      * @return bool
      */
-    public function active()
+    public function active(): bool
     {
-        return is_null($this->endAt) || $this->onGracePeriod();
+        return is_null($this->ends_at) || $this->onGracePeriod();
     }
 
     /**
@@ -142,9 +137,9 @@ public function active()
      *
      * @return bool
      */
-    public function cancelled()
+    public function cancelled(): bool
     {
-        return !is_null($this->endAt);
+        return !is_null($this->ends_at);
     }
 
     /**
@@ -152,10 +147,10 @@ public function cancelled()
      *
      * @return bool
      */
-    public function onTrial()
+    public function onTrial(): bool
     {
-        if (!is_null($this->trialEndAt)) {
-            return Carbon::today()->lt($this->trialEndAt);
+        if (!is_null($this->trial_ends_at)) {
+            return Carbon::today()->lt($this->trial_ends_at);
         } else {
             return false;
         }
@@ -166,9 +161,9 @@ public function onTrial()
      *
      * @return bool
      */
-    public function onGracePeriod()
+    public function onGracePeriod(): bool
     {
-        if (!is_null($endAt = $this->endAt)) {
+        if (!is_null($endAt = $this->ends_at)) {
             return Carbon::now()->lt(Carbon::instance($endAt));
         } else {
             return false;
@@ -182,7 +177,7 @@ public function onGracePeriod()
      *
      * @return $this
      */
-    public function incrementQuantity($count = 1)
+    public function incrementQuantity(int $count = 1)
     {
         $this->updateQuantity($this->quantity + $count);
 
@@ -196,7 +191,7 @@ public function incrementQuantity($count = 1)
      *
      * @return $this
      */
-    public function incrementAndInvoice($count = 1)
+    public function incrementAndInvoice(int $count = 1)
     {
         $this->incrementQuantity($count);
         $this->user->invoice();
@@ -211,7 +206,7 @@ public function incrementAndInvoice($count = 1)
      *
      * @return $this
      */
-    public function decrementQuantity($count = 1)
+    public function decrementQuantity(int $count = 1)
     {
         $this->updateQuantity(max(1, $this->quantity - $count));
 
@@ -225,7 +220,7 @@ public function decrementQuantity($count = 1)
      *
      * @return $this
      */
-    public function updateQuantity($quantity)
+    public function updateQuantity(int $quantity)
     {
         $subscription = $this->asStripeSubscription();
         $subscription->quantity = $quantity;
@@ -253,7 +248,7 @@ public function noProrate()
     /**
      * Change the billing cycle anchor on a plan change.
      *
-     * @param  int|string $date
+     * @param int|string $date
      *
      * @return $this
      */
@@ -271,11 +266,11 @@ public function anchorBillingCycleOn($date = 'now')
     /**
      * Swap the subscription to a new Stripe plan.
      *
-     * @param  string $plan
+     * @param string $plan
      *
      * @return $this
      */
-    public function swap($plan)
+    public function swap(string $plan)
     {
         $subscription = $this->asStripeSubscription();
 
@@ -291,7 +286,7 @@ public function swap($plan)
         // to maintain the current trial state, whether that is "active" or to run
         // the swap out with the exact number of days left on this current plan.
         if ($this->onTrial()) {
-            $subscription->trial_end = $this->trialEndAt->getTimestamp();
+            $subscription->trial_end = $this->trial_ends_at->getTimestamp();
         } else {
             $subscription->trial_end = 'now';
         }
@@ -307,8 +302,8 @@ public function swap($plan)
 
         $this->user->invoice();
 
-        $this->stripePlan = $plan;
-        $this->endAt = null;
+        $this->stripe_plan = $plan;
+        $this->ends_at = null;
         $this->save();
 
         return $this;
@@ -329,9 +324,9 @@ public function cancel()
         // would have ended. Otherwise, we'll retrieve the end of the billing period
         // period and make that the end of the grace period for this current user.
         if ($this->onTrial()) {
-            $this->endAt = $this->trialEndAt;
+            $this->ends_at = $this->trial_ends_at;
         } else {
-            $this->endAt = Carbon::createFromTimestamp(
+            $this->ends_at = Carbon::createFromTimestamp(
                 $subscription->current_period_end
             );
         }
@@ -360,9 +355,9 @@ public function cancelNow()
     /**
      * Mark the subscription as cancelled.
      */
-    public function markAsCancelled()
+    public function markAsCancelled(): void
     {
-        $this->endAt = Carbon::now();
+        $this->ends_at = Carbon::now();
         $this->save();
     }
 
@@ -384,10 +379,10 @@ public function resume()
         // To resume the subscription we need to set the plan parameter on the Stripe
         // subscription object. This will force Stripe to resume this subscription
         // where we left off. Then, we'll set the proper trial ending timestamp.
-        $subscription->plan = $this->stripePlan;
+        $subscription->plan = $this->stripe_plan;
 
         if ($this->onTrial()) {
-            $subscription->trial_end = $this->trialEndAt->getTimestamp();
+            $subscription->trial_end = $this->trial_ends_at->getTimestamp();
         } else {
             $subscription->trial_end = 'now';
         }
@@ -397,7 +392,7 @@ public function resume()
         // Finally, we will remove the ending timestamp from the user's record in the
         // local database to indicate that the subscription is active again and is
         // no longer "cancelled". Then we will save this record in the database.
-        $this->endAt = null;
+        $this->ends_at = null;
         $this->save();
 
         return $this;
@@ -410,6 +405,6 @@ public function resume()
      */
     public function asStripeSubscription()
     {
-        return $this->user->asStripeCustomer()->subscriptions->retrieve($this->stripeId);
+        return $this->user->asStripeCustomer()->subscriptions->retrieve($this->stripe_id);
     }
 }
diff --git a/tests/CashierTest.php b/tests/CashierTest.php
index 413fc59..5f78d2d 100644
--- a/tests/CashierTest.php
+++ b/tests/CashierTest.php
@@ -32,7 +32,7 @@ public function testSubscriptionsCanBeCreated()
         $user->newSubscription('main', 'monthly-10-1')->create($this->getTestToken());
 
         $this->assertEquals(1, count($user->subscriptions));
-        $this->assertNotNull($user->subscription('main')->stripeId);
+        $this->assertNotNull($user->subscription('main')->stripe_id);
         $this->assertTrue($user->subscribed('main'));
         $this->assertTrue($user->subscribedToPlan('monthly-10-1', 'main'));
         $this->assertFalse($user->subscribedToPlan('monthly-10-1', 'something'));
@@ -52,13 +52,13 @@ public function testSubscriptionsCanBeCreated()
         $this->assertTrue($subscription->onGracePeriod());
 
         // Modify Ends Date To Past
-        $oldGracePeriod = $subscription->endAt;
-        $subscription->updateAttributes(['endAt' => Carbon::now()->subDays(5)]);
+        $oldGracePeriod = $subscription->ends_at;
+        $subscription->updateAttributes(['ends_at' => Carbon::now()->subDays(5)]);
 
         $this->assertFalse($subscription->active());
         $this->assertTrue($subscription->cancelled());
         $this->assertFalse($subscription->onGracePeriod());
-        $subscription->updateAttributes(['endAt' => $oldGracePeriod]);
+        $subscription->updateAttributes(['ends_at' => $oldGracePeriod]);
 
         // Resume Subscription
         $subscription->resume();
@@ -79,7 +79,7 @@ public function testSubscriptionsCanBeCreated()
         // Swap Plan
         $subscription->swap('monthly-10-2');
 
-        $this->assertEquals('monthly-10-2', $subscription->stripePlan);
+        $this->assertEquals('monthly-10-2', $subscription->stripe_plan);
 
         // Invoice Tests
         $invoice = $user->invoices()[1];
@@ -97,7 +97,9 @@ public function testCreatingSubscriptionWithCoupons()
 
         // Create Subscription
         $user->newSubscription('main', 'monthly-10-1')
-            ->withCoupon('coupon-1')->create($this->getTestToken());
+            ->withCoupon('coupon-1')
+            ->create($this->getTestToken());
+
         $subscription = $user->subscription('main');
 
         $this->assertTrue($user->subscribed('main'));
@@ -120,9 +122,11 @@ public function testGenericTrials()
     {
         $user = new User();
         $this->assertFalse($user->onGenericTrial());
-        $user->trialEndAt = Carbon::tomorrow();
+
+        $user->trial_ends_at = Carbon::tomorrow();
         $this->assertTrue($user->onGenericTrial());
-        $user->trialEndAt = Carbon::today()->subDays(5);
+
+        $user->trial_ends_at = Carbon::today()->subDays(5);
         $this->assertFalse($user->onGenericTrial());
     }
 
@@ -132,12 +136,14 @@ public function testCreatingSubscriptionWithTrial()
 
         // Create Subscription
         $user->newSubscription('main', 'monthly-10-1')
-            ->trialDays(7)->create($this->getTestToken());
+            ->trialDays(7)
+            ->create($this->getTestToken());
+
         $subscription = $user->subscription('main');
 
         $this->assertTrue($subscription->active());
         $this->assertTrue($subscription->onTrial());
-        $this->assertEquals(Carbon::today()->addDays(7)->day, $subscription->trialEndAt->day);
+        $this->assertEquals(Carbon::today()->addDays(7)->day, $subscription->trial_ends_at->day);
 
         // Cancel Subscription
         $subscription->cancel();
@@ -151,7 +157,7 @@ public function testCreatingSubscriptionWithTrial()
         $this->assertTrue($subscription->active());
         $this->assertFalse($subscription->onGracePeriod());
         $this->assertTrue($subscription->onTrial());
-        $this->assertEquals(Carbon::today()->addDays(7)->day, $subscription->trialEndAt->day);
+        $this->assertEquals(Carbon::today()->addDays(7)->day, $subscription->trial_ends_at->day);
     }
 
     public function testApplyingCouponsToExistingCustomers()
@@ -181,8 +187,8 @@ public function testMarkingAsCancelledFromWebhook()
             'type' => 'customer.subscription.deleted',
             'data' => [
                 'object' => [
-                    'id' => $subscription->stripeId,
-                    'customer' => $user->stripeId,
+                    'id' => $subscription->stripe_id,
+                    'customer' => $user->stripe_id,
                 ],
             ],
         ]);
diff --git a/tests/TestCase.php b/tests/TestCase.php
index 4026ee9..c18f2f4 100644
--- a/tests/TestCase.php
+++ b/tests/TestCase.php
@@ -85,30 +85,30 @@ protected function setupTestDbData()
 
         // Structure :
 
-        $db->createCommand()->createTable('subscription', [
+        $db->createCommand()->createTable('subscriptions', [
             'id' => 'pk',
-            'userId' => 'integer not null',
+            'user_id' => 'integer not null',
             'name' => 'string not null',
-            'stripeId' => 'string not null',
-            'stripePlan' => 'string not null',
+            'stripe_id' => 'string not null',
+            'stripe_plan' => 'string not null',
             'quantity' => 'integer not null',
-            'trialEndAt' => 'timestamp null default null',
-            'endAt' => 'timestamp null default null',
-            'createdAt' => 'timestamp null default null',
-            'updatedAt' => 'timestamp null default null',
+            'trial_ends_at' => 'timestamp null default null',
+            'ends_at' => 'timestamp null default null',
+            'created_at' => 'timestamp null default null',
+            'updated_at' => 'timestamp null default null',
         ])->execute();
 
-        $db->createCommand()->createTable('user', [
+        $db->createCommand()->createTable('users', [
             'id' => 'pk',
             'username' => 'string',
             'email' => 'string',
-            'stripeId' => 'string',
-            'cardBrand' => 'string',
-            'cardLastFour' => 'string',
-            'trialEndAt' => 'timestamp null default null',
+            'stripe_id' => 'string',
+            'card_brand' => 'string',
+            'card_last_four' => 'string',
+            'trial_ends_at' => 'timestamp null default null',
         ])->execute();
 
-        $db->createCommand()->insert('user', [
+        $db->createCommand()->insert('users', [
             'username' => 'John Doe',
             'email' => 'johndoe@domain.com',
         ])->execute();
diff --git a/tests/data/User.php b/tests/data/User.php
index f2445db..14cff9e 100644
--- a/tests/data/User.php
+++ b/tests/data/User.php
@@ -20,7 +20,7 @@ class User extends ActiveRecord implements IdentityInterface
      */
     public static function tableName()
     {
-        return 'user';
+        return 'users';
     }
 
     /**