wi fi password doesnt work

The sticker on the device should include two passwords. One is the administrator password and is probably the one labeled as "Password". The other is the password for the WiFi SSID and it might be labeled as "WiFi Key". Assuming you didn't create a new SSID and password when you set up the gateway, then you should use the WiFi Key.

If you have the T-Mobile Home Internet app and you are logged into your router, you can find the password for the network by going to the “Network” tab in the app – click on the network and then click on the eye symbol to the right of the password to show it.