no internet

If the message is connected but no internet the cellular signals may be down. It could be the gateway does not receive the cellular signals OR it might be a possible SIM card issue. Usually if there is a problem with the SIM card it will produce an error condition. Scroll through the menu options on the LED screen to see if there are any alarms or notifications reported. If you cannot see clear indication the cellular signal(s) are delivered it might be worth reseating the SIM. To do so you would want to first power off the gateway. After it is powered down then you can carefully remove and re-insert the SIM card into the tray. The SIM card has a notch on one corner and only fits into the SIM carrier in the single orientation. After the SIM is reseated power it up and watch the LED screen. If you see the bars reporting the signal strength for the cellular connections then you should/may be good to go. 

I have seen the same messaging when the cellular signals are down. Sometimes a gateway reboot will allow the gateway to connect again. If the problem is with no signal from the tower then a reboot nor investigation with the SIM will help. Then it is time to check https://downdetector.com from another device that has internet service and check if service is up or down. If it is down all you can do is call T-Mobile and wait. If there is an alien invasion take cover.