Login to custom API via imx/login not allowed

Hello,

we have a simple Custom API which allows an authentication via RoleBasedPerson:

public Task<IEnumerable<IMethodSet>> GetMethodSetsAsync(CancellationToken ct = new CancellationToken())
        {
            var methodSet = new MethodSet
            {
                AppId = "CustomService",
                SessionConfig = new SessionAuthDbConfig { AuthenticationType = AuthType.AllManualModules }
            };

            methodSet.Configure(_resolver, new IApiProvider[]
            {
                new ...
            });

            return Task.FromResult<IEnumerable<IMethodSet>>(new[]
            {
                methodSet
            });
        }

When we try to login via username and password of an Identity, we get "You do not have permission to log in.".

For any other Custom API with the same SessionConfig, its no problem to authenticate with the user.