A non-empty PSR-4 prefix must end with a namespace separator

Someone made a comment but removed it. He mentioned I was missing \\ at the end of Acme\\models. Acme\\models\\ will get rid of the message and work as it should.

As others said PSR-4 requires the trailing slash

Though I had to convert / to \\ in Windows (should work fine on Linux):

    "autoload": {
        "psr-4": {
            "App\\": "src/"
        }
    },
    "autoload-dev": {
        "psr-4": {
            "App\\Tests\\": "tests/"
        }
    },