Printer connection

Some devices cannot connect to the gateway’s default network.  You want to leave this network alone and ADD a second network with the + sign at the bottom of the Network tab in the T-Mobile Internet app.  For this new network, set the band to 2.4 GHz and set the WPA version to WPA/WPA2.  Try connecting your printer to this second network.  Use the default network for your other devices, as much as possible.

Here are the T-Mobile support instructions for how to add the second network with the app.

Android  How to create additional Wi-Fi networks | T-Mobile Internet app | Android | T-Mobile Support

iOS  How to create additional Wi-Fi networks | T-Mobile Internet app | iOS | T-Mobile Support