if ( ! empty( $request['topic'] ) ) {
            if ( wc_is_webhook_valid_topic( strtolower( $request['topic'] ) ) ) {
                $webhook->set_topic( $request['topic'] );
            } else {
                return new WP_Error( "woocommerce_rest_{$this->post_type}_invalid_topic", __( 'Webhook topic must be valid.', 'woocommerce' ), array( 'status' => 400 ) );