diff --git a/tests/integration/API/CacheableAPIBaseTest.php b/tests/integration/API/CacheableAPIBaseTest.php
index 95729b3c4..563060743 100644
--- a/tests/integration/API/CacheableAPIBaseTest.php
+++ b/tests/integration/API/CacheableAPIBaseTest.php
@@ -25,7 +25,7 @@ class CacheableAPIBaseTest extends \Codeception\TestCase\WPTestCase {
 	 *
 	 * @throws ReflectionException
 	 */
-	public function test_do_remote_request( bool $is_cacheable, bool $force_refresh = null, bool $cache_exists = null, bool $should_load_from_cache = false ) {
+	public function test_do_remote_request( bool $is_cacheable, ?bool $force_refresh = null, ?bool $cache_exists = null, bool $should_load_from_cache = false ) {
 
 		$request = $this->get_new_request_instance( $is_cacheable );
 
@@ -357,7 +357,7 @@ public function provider_get_request_cache_lifetime(): array {
 	 *
 	 * @throws ReflectionException
 	 */
-	public function test_get_request_data_for_broadcast( bool $is_cacheable, bool $force_refresh = null, bool $should_cache = null ) {
+	public function test_get_request_data_for_broadcast( bool $is_cacheable, ?bool $force_refresh = null, ?bool $should_cache = null ) {
 
 		$request = $this->get_new_request_instance( $is_cacheable );
 
diff --git a/woocommerce/Helpers/OrderHelper.php b/woocommerce/Helpers/OrderHelper.php
index 52f7a36a8..3d2862234 100644
--- a/woocommerce/Helpers/OrderHelper.php
+++ b/woocommerce/Helpers/OrderHelper.php
@@ -78,7 +78,7 @@ public static function get_customer_id( \WC_Order $order ) {
 	 * @param mixed     $default    Optional. The default value if the property doesn't exist. Default null.
 	 * @return mixed The property value if found, or the default value if not found.
 	 */
-	public static function get_property( \WC_Order $order, string $key, $nested_key = null, $default = null ): mixed {
+	public static function get_property( \WC_Order $order, string $key, $nested_key = null, $default = null ) {
 		return Dynamic_Props::get( $order, $key, $nested_key, $default );
 	}
 
diff --git a/woocommerce/payment-gateway/Dynamic_Props.php b/woocommerce/payment-gateway/Dynamic_Props.php
index 609ed2107..6ccf833be 100644
--- a/woocommerce/payment-gateway/Dynamic_Props.php
+++ b/woocommerce/payment-gateway/Dynamic_Props.php
@@ -42,7 +42,7 @@ class Dynamic_Props {
 	 * @since x.x.x
 	 * @var   \WeakMap<object, \stdClass>|null
 	 */
-	private static ?\WeakMap $map = null;
+	private static ?\WeakMap $map = null; // phpcs:ignore PHPCompatibility.Classes.NewClasses.weakmapFound -- conditionally used for PHP 8.0+
 
 	/**
 	 * Sets a property on the order object.
@@ -64,7 +64,7 @@ class Dynamic_Props {
 	 * Dynamic_Props::set($order, 'payment_total', '99.99');
 	 * ```
 	 */
-	public static function set( \WC_Order &$order, string $key, mixed $value ): void {
+	public static function set( \WC_Order &$order, string $key, $value ): void {
 		if ( self::use_weak_map() ) {
 			self::init_weak_map();
 			if ( ! isset( self::$map[ $order ] ) ) {
@@ -97,7 +97,7 @@ public static function set( \WC_Order &$order, string $key, mixed $value ): void
 	 * $token       = Dynamic_Props::get($order, 'payment', 'token', 'DEFAULT_TOKEN');
 	 * ```
 	 */
-	public static function get( \WC_Order $order, string $key, $nested_key = null, $default = null ): mixed {
+	public static function get( \WC_Order $order, string $key, $nested_key = null, $default = null ) {
 		if ( self::use_weak_map() ) {
 			self::init_weak_map();
 			if ( is_null( $nested_key ) ) {
@@ -184,6 +184,7 @@ private static function use_weak_map(): bool {
 	 */
 	private static function init_weak_map(): void {
 		if ( null === self::$map ) {
+			// phpcs:ignore PHPCompatibility.Classes.NewClasses.weakmapFound -- conditionally used for PHP 8.0+
 			self::$map = new \WeakMap();
 		}
 	}
diff --git a/woocommerce/payment-gateway/class-sv-wc-payment-gateway-direct.php b/woocommerce/payment-gateway/class-sv-wc-payment-gateway-direct.php
index 4185a7c26..50b5fe054 100644
--- a/woocommerce/payment-gateway/class-sv-wc-payment-gateway-direct.php
+++ b/woocommerce/payment-gateway/class-sv-wc-payment-gateway-direct.php
@@ -484,7 +484,7 @@ protected function get_notices_as_user_messages( ?string $type = null ) : array
 				$message = $notice['notice'] ?? $notice;
 
 				// this will handle some log data eventually
-				$messages[] = htmlspecialchars( is_array( $message ) ? print_r( $message, true ) : $message );
+				$messages[] = htmlspecialchars( is_array( $message ) ? print_r( $message, true ) : $message, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML401 );
 			}
 		}
 
diff --git a/woocommerce/payment-gateway/class-sv-wc-payment-gateway.php b/woocommerce/payment-gateway/class-sv-wc-payment-gateway.php
index 39de01002..c821269fe 100755
--- a/woocommerce/payment-gateway/class-sv-wc-payment-gateway.php
+++ b/woocommerce/payment-gateway/class-sv-wc-payment-gateway.php
@@ -3753,12 +3753,12 @@ public function add_debug_message( $message, ?string $type = 'message' ) : void
 
 			if ( 'message' === $type ) {
 
-				SV_WC_Helper::wc_add_notice( str_replace( "\n", "<br/>", htmlspecialchars( $message ) ), 'notice' );
+				SV_WC_Helper::wc_add_notice( str_replace( "\n", "<br/>", htmlspecialchars( $message, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML401 ) ), 'notice' );
 
 			} else {
 
 				// defaults to error message
-				SV_WC_Helper::wc_add_notice( str_replace( "\n", "<br/>", htmlspecialchars( $message ) ), 'error' );
+				SV_WC_Helper::wc_add_notice( str_replace( "\n", "<br/>", htmlspecialchars( $message, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML401 ) ), 'error' );
 			}
 		}
 	}