Fatal error: Uncaught Error: Interface "Http\Promise\Promise" not found in /var/www/html1/wp-content/plugins/zettle-pos-integration/vendor/php-http/httplug/src/Promise/HttpFulfilledPromise.php:9 Stack trace: #0 {main} thrown in /var/www/html1/wp-content/plugins/zettle-pos-integration/vendor/php-http/httplug/src/Promise/HttpFulfilledPromise.php on line 9