1) Make sure the SIM is inserted correctly.
a) If the SIM is inserted correctly, check to see if 4G, 3G or 2G is displayed on the top left of the screen of your watch.
b) If not, try restarting your watch.
2) If 4G, 3G or 2G is displayed, check to make sure there are no overdue network charges that need to be paid.
3) Check if the watch is connected to the cellular network and in arrears.