Website to connect with Hotel Wlan opens?

If I select the correct wlan and enter the correct PIN, comes a notification with "sign in wlan" or "wlan authorize". Both come with an error message "The website is not available" (see photo). Have already researched on the Internet but all solutions such as mobile down and drive up again have brought nothing. Have a P 20 Pro from Huawei.

Go to the reception and ask.

Why do not you ask at the reception?

My tip would be the wireless is overloaded or too weak in your room.