Connected device not assigned IP address

SOLVED: T-Mobile tech support was unable to help or even suggest anything. It turns out that the computer (which doesn't support Wi-Fi and thus was connected to the T-Mobile unit via an ethernet wire) was configured to accept DHCP IP assignments with either or both IPV4 and IPV6 IP addresses.  Unfortunately the T-Mobile Home Internet router saw that and assigned an IPV6 address to the computer instead of an IPv4 address like it did for all the other devices on the local network. The phone app, which is the only interface to the T-Mobile Home Internet router, can't or won't display IPV6 addresses.  Plus it is such a minimal router interface that there is no way to tell it to only assign IPv4 addresses or to specify that it assign a static address to a device.

The solution for me was to connect the computer to my old router, connect to it, and discover and then change its configuration to not allow the use of IPv6.  Then with the computer re-connected to the T-Mobile router it had no choice but to assign an IPv4 address which the app could then display to me. Problem solved, however, it pointed out to me that there are signficant deficits in the T-Mobile router and user-interface.