Don't add notices during REST requests

woocommerce/changelog.txt

@@ -1,6 +1,7 @@
 *** SkyVerge WooCommerce Plugin Framework Changelog ***
 
 2026.nn.nn - version 6.2.2
+* Fix - Failed transaction attempt causes future attempts to fail when using Block checkout
 
 2026.05.18 - version 6.2.1
 * Fix - Protect against `ScriptHelper` fatal errors on plugin upgrades

woocommerce/payment-gateway/class-sv-wc-payment-gateway.php

@@ -3070,17 +3070,22 @@ public function mark_order_as_failed( $order, $error_message, $response = null )
 
 		$this->add_debug_message( $error_message, 'error' );
 
-		$user_message = '';
+		// In Store API / REST context the message is returned in the process_payment()
+		// result and surfaced via RouteException; adding a session notice here leaks
+		// into the next request's cart validation (woocommerce_rest_cart_item_error 409).
+		if ( ! SV_WC_Helper::is_rest_api_request() ) {
+			$user_message = '';
+
+			if ( $response && $this->is_detailed_customer_decline_messages_enabled() ) {
+				$user_message = $response->get_user_message();
+			}
 
-		if ( $response && $this->is_detailed_customer_decline_messages_enabled() ) {
-			$user_message = $response->get_user_message();
-		}
+			if ( ! $user_message ) {
+				$user_message = esc_html__( 'An error occurred, please try again or try an alternate form of payment.', 'woocommerce-plugin-framework' );
+			}
 
-		if ( ! $user_message ) {
-			$user_message = esc_html__( 'An error occurred, please try again or try an alternate form of payment.', 'woocommerce-plugin-framework' );
+			SV_WC_Helper::wc_add_notice( $user_message, 'error' );
 		}
-
-		SV_WC_Helper::wc_add_notice( $user_message, 'error' );
 	}
 
 
@@ -3750,6 +3755,13 @@ public function add_debug_message( $message, ?string $type = 'message' ) : void
 			return;
 		}
 
+		// avoid adding notices on Store API / REST requests; the message is already returned in the
+		// response body and a session notice would leak into the next cart-validation request and
+		// surface as a 409 woocommerce_rest_cart_item_error.
+		if ( SV_WC_Helper::is_rest_api_request() ) {
+			return;
+		}
+
 		// add debug message to woocommerce->errors/messages if checkout or both is enabled, the admin/Ajax check ensures capture charge transactions aren't logged as notices to the front end
 		if ( ( $this->debug_checkout() || ( 'error' === $type && $this->is_test_environment() ) ) && ( ! is_admin() || wp_doing_ajax() ) ) {