When installing API Platform using Composer with
composer req api for example and you get version 2.7 installed make sure that when following the documentation of API Platform (having
ApiPlatform\Metadata\ApiResource as attribute) you also put the directive
metadata_backward_compatibility_layer: false under
api/config/packages/api_platform.yaml otherwise your resources won't be available.
See https://api-platform.com/docs/v3.0/core/upgrade-guide/ for more information.