Change order state to failed when receive the order declined webhook

src/Mondu/Mondu/Controllers/WebhooksController.php

@@ -164,6 +164,12 @@ private function handle_declined( $params ) {
 			return $this->return_not_found();
 		}
 
+		$order->add_order_note( esc_html( sprintf( __( 'Mondu order is on declined state.', 'mondu' ) ) ), false );
+
+		if ( $order->get_status() == 'on-hold' ) {
+			$order->update_status('wc-failed', __('Failed', 'woocommerce'));
+		}
+
 		return $this->return_success();
 	}