Fatal error: Uncaught Error: Interface "Psr\Http\Client\ClientInterface" not found in /var/www/html1/wp-content/plugins/zettle-pos-integration/vendor/php-http/httplug/src/HttpClient.php:15 Stack trace: #0 {main} thrown in /var/www/html1/wp-content/plugins/zettle-pos-integration/vendor/php-http/httplug/src/HttpClient.php on line 15