Laravel 5.2 - Mollie API - webhook not working

Question

I'm trying to do do sometype of "Premium" system on my webapp, however I'm having troubles with handling the payment.

I'm using the Mollie Api and I found THIS on github that integrates it into laravel.

public function postMedium()
{
    $user_id = Auth::user()->id;
    $payment = Mollie::getPayments()->create([
        "amount"      => 9.99,
        "description" => "Foodtruck Bestellen Premium - 1 Month",
        "webhookUrl"  => "URL",
        "redirectUrl" => "URL",
        "metadata"    => array(
            'user_id' => $user_id
        )
    ]);
    return redirect($payment->links->paymentUrl);
}


public function mediumPaymentCheck(Request $request)
{
    $payment = Mollie::getPayments()->get(Input::get('id'));
    if ($payment->isPaid()) {

        $user_id = $payment->user_id;

        $user = User::find($user_id);

        $user->premium = true;
        $user->premium_type = "medium";
        $user->premium_expiry_date = Carbon::now()->addDays(30);

        $user->save();
    }
}

After the payment you get redirected to the redirectUrl and that works.

However...

Nothing changes in my DB, so it seems like my webhook url ("mediumPaymentCheck") is being ignored or not working for some reason.

I hope someone can help me out!

Edit: my webhook url looks like this:

Route::group(['middleware' => ['web']], function () {
Route::post('/premium/payment/medium/check', 'PremiumController@mediumPaymentCheck');