Fatal error: Uncaught Error: Class "Flarum\Api\Serializer\AbstractSerializer" not found in /opt/lampp/htdocs/forum/flarum/vendor/fof/oauth/src/Api/Serializers/ProviderSerializer.php:16 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/forum/flarum/vendor/fof/oauth/src/Api/Serializers/ProviderSerializer.php on line 16