From 85e74d4284b78d743c19f1186bbbfcd4d4944d9d Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Wed, 27 Mar 2024 13:49:32 +0100
Subject: [PATCH 01/11] Replace Numbers with their constants value

---
 src/contracts/bsv20LendingPool.ts | 35 ++++++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/src/contracts/bsv20LendingPool.ts b/src/contracts/bsv20LendingPool.ts
index 4d52faf9..e87fe60b 100644
--- a/src/contracts/bsv20LendingPool.ts
+++ b/src/contracts/bsv20LendingPool.ts
@@ -3,6 +3,7 @@ import {
     assert,
     ByteString,
     byteString2Int,
+    Constants,
     fill,
     FixedArray,
     hash256,
@@ -138,9 +139,23 @@ export class Bsv20LendingPool extends BSV20V2 {
 
         // Make sure second input spends collateral holding contract.
         const prevTxId = this.ctx.utxo.outpoint.txid
-        const prevoutCollateralContract = slice(this.prevouts, 36n, 72n)
-        assert(slice(prevoutCollateralContract, 0n, 32n) == prevTxId)
-        assert(byteString2Int(slice(prevoutCollateralContract, 32n, 36n)) == 1n)
+        const prevoutCollateralContract = slice(
+            this.prevouts,
+            Constants.OutpointLen,
+            Constants.OutpointLen * 2n
+        )
+        assert(
+            slice(prevoutCollateralContract, 0n, Constants.TxIdLen) == prevTxId
+        )
+        assert(
+            byteString2Int(
+                slice(
+                    prevoutCollateralContract,
+                    Constants.TxIdLen,
+                    Constants.OutpointLen
+                )
+            ) == 1n
+        )
 
         // Check merkle proof.
         const prevTxid = Sha256(this.ctx.utxo.outpoint.txid)
@@ -173,12 +188,15 @@ export class Bsv20LendingPool extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 72n, 108n) == slice(oracleMsg, 0n, 36n),
+            slice(this.prevouts, Constants.OutpointLen * 2n, 108n) ==
+                slice(oracleMsg, 0n, Constants.OutpointLen),
             'third input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Check token amount is correct.
         assert(utxoTokenAmt == amt, 'invalid token amount')
@@ -322,12 +340,15 @@ export class Bsv20LendingPool extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 72n, 108n) == slice(oracleMsg, 0n, 36n),
+            slice(this.prevouts, Constants.OutpointLen * 2n, 108n) ==
+                slice(oracleMsg, 0n, Constants.OutpointLen),
             'third input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Check token amount is correct.
         const interest = (borrower.amt * this.interestRate) / 100n

From faa6fa5a1708e750db119623326463e4b99dd8ff Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Fri, 29 Mar 2024 18:13:27 +0100
Subject: [PATCH 02/11] Update bsv20Auction.ts

---
 src/contracts/bsv20Auction.ts | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/contracts/bsv20Auction.ts b/src/contracts/bsv20Auction.ts
index 401ec664..02776542 100644
--- a/src/contracts/bsv20Auction.ts
+++ b/src/contracts/bsv20Auction.ts
@@ -12,6 +12,7 @@ import {
     slice,
     StatefulNext,
     pubKey2Addr,
+    Constants,
 } from 'scrypt-ts'
 import { BSV20V2, OrdiMethodCallOptions } from 'scrypt-ord'
 
@@ -105,7 +106,8 @@ export class BSV20Auction extends BSV20V2 {
 
         // Ensure the first input is spending the auctioned ordinal UTXO.
         assert(
-            slice(this.prevouts, 0n, 36n) == this.ordinalPrevout,
+            slice(this.prevouts, 0n, Constants.OutpointLen) ==
+                this.ordinalPrevout,
             'first input is not spending specified ordinal UTXO'
         )
 

From 8548b4ffee6b269b363caa1eda4398c4c584d97b Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Fri, 29 Mar 2024 18:16:00 +0100
Subject: [PATCH 03/11] Update bsv20BuyLimitOrder.ts

---
 src/contracts/bsv20BuyLimitOrder.ts | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/contracts/bsv20BuyLimitOrder.ts b/src/contracts/bsv20BuyLimitOrder.ts
index dbc1d50a..6665514f 100644
--- a/src/contracts/bsv20BuyLimitOrder.ts
+++ b/src/contracts/bsv20BuyLimitOrder.ts
@@ -13,6 +13,7 @@ import {
     assert,
     len,
     byteString2Int,
+    Constants,
 } from 'scrypt-ts'
 import { RabinPubKey, RabinSig, RabinVerifier } from 'scrypt-ts-lib'
 
@@ -71,12 +72,18 @@ export class BSV20BuyLimitOrder extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Check token amount doesn't exceed total.
         const remainingToClear = this.tokenAmt - this.tokenAmtCleared

From 76a6eef1d0a1981c7ab1d6021a550b6e3e2a8204 Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Fri, 29 Mar 2024 18:18:19 +0100
Subject: [PATCH 04/11] Update bsv20BuyOrder.ts

---
 src/contracts/bsv20BuyOrder.ts | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/contracts/bsv20BuyOrder.ts b/src/contracts/bsv20BuyOrder.ts
index 5ccd4026..9a99ad51 100644
--- a/src/contracts/bsv20BuyOrder.ts
+++ b/src/contracts/bsv20BuyOrder.ts
@@ -12,6 +12,7 @@ import {
     pubKey2Addr,
     assert,
     len,
+    Constants,
 } from 'scrypt-ts'
 import { RabinPubKey, RabinSig, RabinVerifier } from 'scrypt-ts-lib'
 
@@ -60,7 +61,11 @@ export class BSV20BuyOrder extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 

From 34436cb3bdbc19b8a3092ae67f315ff7d63b9dac Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Fri, 29 Mar 2024 18:25:06 +0100
Subject: [PATCH 05/11] Update bsv20CouponBond.ts

---
 src/contracts/bsv20CouponBond.ts | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/src/contracts/bsv20CouponBond.ts b/src/contracts/bsv20CouponBond.ts
index 8c6e75dd..86a9193f 100644
--- a/src/contracts/bsv20CouponBond.ts
+++ b/src/contracts/bsv20CouponBond.ts
@@ -3,6 +3,7 @@ import {
     assert,
     ByteString,
     byteString2Int,
+    Constants,
     fill,
     FixedArray,
     hash256,
@@ -101,12 +102,18 @@ export class Bsv20CouponBond extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Ensure token amount is equal to the face value.
         assert(utxoTokenAmt == this.faceValue, 'utxo token amount insufficient')
@@ -152,7 +159,11 @@ export class Bsv20CouponBond extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
@@ -173,7 +184,9 @@ export class Bsv20CouponBond extends BSV20V2 {
         }
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Ensure utxo token amount covers output token amount.
         assert(utxoTokenAmt >= totalAmt, 'utxo token amount insufficient')
@@ -199,7 +212,11 @@ export class Bsv20CouponBond extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
@@ -219,7 +236,9 @@ export class Bsv20CouponBond extends BSV20V2 {
         }
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Ensure utxo token amount covers output token amount.
         assert(utxoTokenAmt >= totalAmt, 'utxo token amount insufficient')

From 9d6133e5b5afa2c08803563bc6d8b8e99ea1b25b Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Sun, 31 Mar 2024 12:54:49 +0100
Subject: [PATCH 06/11] Update bsv20ForwardContract.ts

---
 src/contracts/bsv20ForwardContract.ts | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/contracts/bsv20ForwardContract.ts b/src/contracts/bsv20ForwardContract.ts
index 004ed026..44742f0e 100644
--- a/src/contracts/bsv20ForwardContract.ts
+++ b/src/contracts/bsv20ForwardContract.ts
@@ -1,4 +1,3 @@
-import { assert } from 'console'
 import { BSV20V2 } from 'scrypt-ord'
 import {
     ByteString,
@@ -11,6 +10,8 @@ import {
     Sig,
     slice,
     Utils,
+    assert,
+    Constants,
 } from 'scrypt-ts'
 import { RabinPubKey, RabinSig, RabinVerifier } from 'scrypt-ts-lib'
 
@@ -120,12 +121,18 @@ export class Bsv20ForwardContract extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Check token amount is correct.
         assert(utxoTokenAmt == this.amt, 'invalid token amount')

From 2a44cced4beb6d6506fb719ed7e1000795f75f33 Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Sun, 31 Mar 2024 12:57:01 +0100
Subject: [PATCH 07/11] Update bsv20LendingPoolCollateral.ts

---
 src/contracts/bsv20LendingPoolCollateral.ts | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/contracts/bsv20LendingPoolCollateral.ts b/src/contracts/bsv20LendingPoolCollateral.ts
index 8b1ffbb4..b1a5177a 100644
--- a/src/contracts/bsv20LendingPoolCollateral.ts
+++ b/src/contracts/bsv20LendingPoolCollateral.ts
@@ -1,6 +1,7 @@
 import {
     assert,
     byteString2Int,
+    Constants,
     hash256,
     method,
     prop,
@@ -25,9 +26,13 @@ export class Bsv20LendingPoolCollateral extends SmartContract {
 
         // Make sure first input spends main contract.
         const prevTxId = this.ctx.utxo.outpoint.txid
-        const prevoutContract = slice(this.prevouts, 0n, 36n)
-        assert(slice(prevoutContract, 0n, 32n) == prevTxId)
-        assert(byteString2Int(slice(prevoutContract, 32n, 36n)) == 0n)
+        const prevoutContract = slice(this.prevouts, 0n, Constants.OutpointLen)
+        assert(slice(prevoutContract, 0n, Constants.TxIdLen) == prevTxId)
+        assert(
+            byteString2Int(
+                slice(prevoutContract, Constants.TxIdLen, Constants.OutpointLen)
+            ) == 0n
+        )
 
         // Propagate contract.
         const output = this.buildStateOutput(this.amt)

From 5b104fbc500089bc32dd6e7b65097a7c647a3532 Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Sun, 31 Mar 2024 12:59:34 +0100
Subject: [PATCH 08/11] Update bsv20Loan.ts

---
 src/contracts/bsv20Loan.ts | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/contracts/bsv20Loan.ts b/src/contracts/bsv20Loan.ts
index cbd9a0e8..83acc05b 100644
--- a/src/contracts/bsv20Loan.ts
+++ b/src/contracts/bsv20Loan.ts
@@ -3,6 +3,7 @@ import {
     assert,
     ByteString,
     byteString2Int,
+    Constants,
     hash256,
     method,
     prop,
@@ -104,12 +105,18 @@ export class Bsv20Loan extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Check token amount is correct.
         const interest = (this.tokenAmt * this.interestRate) / 100n

From f9627d9883fe463e728f50b19d70a1ec28ae7f15 Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Sun, 31 Mar 2024 13:04:33 +0100
Subject: [PATCH 09/11] Update bsv20LoanMultiple.ts

---
 src/contracts/bsv20LoanMultiple.ts | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/contracts/bsv20LoanMultiple.ts b/src/contracts/bsv20LoanMultiple.ts
index 702dc9fb..f91878dc 100644
--- a/src/contracts/bsv20LoanMultiple.ts
+++ b/src/contracts/bsv20LoanMultiple.ts
@@ -3,6 +3,7 @@ import {
     assert,
     ByteString,
     byteString2Int,
+    Constants,
     fill,
     FixedArray,
     hash256,
@@ -204,12 +205,18 @@ export class Bsv20LoanMultiple extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Check token amount is correct.
         assert(utxoTokenAmt == borrower.amt, 'invalid token amount')
@@ -256,12 +263,18 @@ export class Bsv20LoanMultiple extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Check token amount is correct.
         assert(utxoTokenAmt == borrower.amt, 'invalid token amount')

From f2b8be204e5f3b9d7d655ae43999540bffe53865 Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Sun, 31 Mar 2024 13:16:15 +0100
Subject: [PATCH 10/11] Update bsv20PutOption.ts

---
 src/contracts/bsv20PutOption.ts | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/contracts/bsv20PutOption.ts b/src/contracts/bsv20PutOption.ts
index 0e65468b..a820cebe 100644
--- a/src/contracts/bsv20PutOption.ts
+++ b/src/contracts/bsv20PutOption.ts
@@ -3,6 +3,7 @@ import {
     assert,
     ByteString,
     byteString2Int,
+    Constants,
     hash256,
     method,
     prop,
@@ -80,12 +81,18 @@ export class Bsv20PutOption extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Check token amount is correct.
         assert(utxoTokenAmt == this.tokenAmt, 'invalid token amount')

From 68de77d91136f9905a939b3c2f5e29539126230d Mon Sep 17 00:00:00 2001
From: Yusuf Idi Maina <120538505+yusufidimaina9989@users.noreply.github.com>
Date: Sun, 31 Mar 2024 13:45:57 +0100
Subject: [PATCH 11/11] Update bsv20ZeroCouponBond.ts

---
 src/contracts/bsv20ZeroCouponBond.ts | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/contracts/bsv20ZeroCouponBond.ts b/src/contracts/bsv20ZeroCouponBond.ts
index 0c7b381b..d13005b4 100644
--- a/src/contracts/bsv20ZeroCouponBond.ts
+++ b/src/contracts/bsv20ZeroCouponBond.ts
@@ -3,6 +3,7 @@ import {
     assert,
     ByteString,
     byteString2Int,
+    Constants,
     fill,
     FixedArray,
     hash256,
@@ -101,12 +102,18 @@ export class Bsv20ZeroCouponBond extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Ensure token amount is equal to the purchase price.
         assert(
@@ -154,7 +161,11 @@ export class Bsv20ZeroCouponBond extends BSV20V2 {
 
         // Check that we're unlocking the UTXO specified in the oracles message.
         assert(
-            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            slice(
+                this.prevouts,
+                Constants.OutpointLen,
+                Constants.OutpointLen * 2n
+            ) == slice(oracleMsg, 0n, Constants.OutpointLen),
             'second input is not spending specified ordinal UTXO'
         )
 
@@ -174,7 +185,9 @@ export class Bsv20ZeroCouponBond extends BSV20V2 {
         }
 
         // Get token amount held by the UTXO from oracle message.
-        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+        const utxoTokenAmt = byteString2Int(
+            slice(oracleMsg, Constants.OutpointLen, 44n)
+        )
 
         // Ensure utxo token amount covers output token amount.
         assert(utxoTokenAmt >= totalAmt, 'utxo token amount insufficient')