Lumen POST Access "MethodNotAllowedHttpException"

Question

The small REST API I made works locally well. When transferring on a server the GET requests all work, but the POST don't.
I have read many people have this effect and the problem most of the time is wrong routing.

Looks like the trailing slash creates a redirect which causes the problem. Without the trailing slash no redirect is done and the POST to the API works.

Is there a way to make this work no matter if a trailing slash or not?

Here is the .htaccess:

<IfModule mod_rewrite.c>
    <IfModule mod_negotiation.c>
        Options -MultiViews -Indexes
    </IfModule>

    RewriteEngine On
    RewriteBase /
    # Handle Authorization Header
    RewriteCond %{HTTP:Authorization} .
    RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]

    # Redirect Trailing Slashes If Not A Folder...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_URI} (.+)/$
    RewriteRule ^ %1 [L,R=301]

    # Handle Front Controller...
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteRule ^ index.php [L]
</IfModule>

Here comes my routing and the controller:

$router->group(['prefix' => 'auth'], function ($router) {
    $router->post('register', 'AuthController@register');
    $router->post('login', 'AuthController@login');
    $router->post('logout', 'AuthController@logout');
    $router->post('refresh', 'AuthController@refresh');
    $router->get('me', 'AuthController@me');
});


class AuthController extends Controller
{
    public function __construct()
    {
        $this->middleware('auth:api', ['except' => ['login', 'register']]);
    }

    public function login(Request $request)
    {
        $credentials = $request->only(['email', 'password']);
        if (!$token = Auth::attempt($credentials)) {
            return response()->json(['error' => 'Unauthorized'], 401);
        }
        return $this->respondWithToken($token);
    }    
}