But it could be that you have to connect your PC with the WiFi and portal before so you can authenticate. After it you need to clone the MAC address of the PC to your router.
Yes, I am aware, that I might have to clone the MAC address.
People who experience that their browser is not forwarded to the captive portal, should try to deactivate “DNS rebinding attack protection” …
One can find the option under:
More Settings > Custom DNS Server
First this happened to me, I wasnt forwarded and I had to clone the MAC of my PC, to be recognized by the wifi service.
But once I deactivated that option, I could just use the “native MAC” of the router, as I was then forwarded to the captive portal and able to authenticate with my account’s username and password.