Should be on the tower.

Assuming you never changed the default password on your TMO router, the password is printed on the label on the bottom of your router. There is another default password for admin, but that one is to login to the router via app for configuration.

Since both are printed, I would recommend you change both wifi and admin passwords.

Thanks for the information. Appreciate it 

The Arcadyan Gateway has the label on the back side and the WIFI and Admin passwords are there.

I’m on an older Mac intel core 10.7.5

tried password on the back of tower. Plus the easier to remember password I use to log in. Always says failed.  Is the WPA2 enterprise credentials different than what’s on the tower or what I changed my password to be??  Where do I find this if so??  Grrrrrrr

What is the  app for router login? 

Same! Has anyone ever resolved this on an older Mac? 

Found something actually, Creating a second SSID on the T-Mobile app at 2.4GHz with WPA/WPA2 authentication helped me with my old MacBook Pro connecting to the internet.

Either Tmobile or TLife app can manage your home internet gateway.