When you come back answer a few questions....
If you purchased your US Roaming add on 10 or more days ago you need to contact customer support to fix a glitch with it not working past 10 days.
@leep yes reboot. power off the phone for a min and power it back up again
if still not work, try this to manually pick T-mobile
Slide your finger downwards starting from the top of the screen.
Press the settings icon.
Press Mobile networks.
Press Network operators.
manually, press Search networks and wait while your phone searches for networks.if you see T-Mobile, select it
@leep which city and state you are at now? are you in a different city or different area from where you had connection?
try a phone reboot
try to manually connect to T-Mobile networks instead of using automatic
and check My Account using Incognito mode to confirm roaming not expired yet