T-Mobile home internet error code 1200

I downloaded the T-Mobile home internet app and I’m connected to its Wi-Fi and am able to go to 192.168.12.1 but when I open the app and try to use it to set it up it says “Uh Oh - your internet app lost connection with your 5g wi-fi gateway gateway and needs to restart. Error code: 1200” and gives me the option to restart the app but nothing changes. Any help would be appreciated.