Connecting Ring to T-Mobile internet

Which T-Mobile gateway are you using?

Short explanation is that you need to configure the T-Mobile gateway to separate the internal WiFi network frequencies (2.4 and 5ghz) into two WiFi networks with individual names, then connect the Ring device to the 2.4ghz network.

The specifics of doing this depend on the model gateway you've got. I have the Nokia, and it is the very easiest one to setup this way. The other models are usually more difficult and someone else would have to help you with that. 

——What follows is lots of background about this problem; feel free to skip.

Most WiFi routers will allow you to setup two separate WiFi networks, one 2.4ghz and one 5ghz, or they will allow you to "combine" them so that they both use the same name/password, and you only have one WiFi network name and password to deal with. In that second case, the router is supposed to figure out what frequency (2.4 or 5) your device can use. If it's a 2.4ghz only device (like many Ring devices), it should connect it to that WiFi frequency, but the T-Mobile gateways seem to have trouble doing that with some of the 2.4ghz Ring devices. AFAIK, T-Mobile's gateways default to that single network model, hence the need to separate them out so that you can connect those problematic Ring devices directly to the 2.4ghz WiFi network.

There are many WiFi routers that don't have that problem. I added an eero mesh network at my house (using the single WiFi name/password) and connected it to the Nokia gateway via an Ethernet cable, and the eero router had no problem properly connecting to any of my Ring devices, even those that my T-Mobile gateway struggled with. 

Also note that my Nokia gateway didn’t have that problem with all my 2.4ghz only devices, but my Ring doorbells did need the separate WiFi networks, until I added the eero mesh network, and the eero router has no problem figuring out which frequency to use with my Ring devices, so now I’m back to the single combined WiFi network name/password