After the activation is done, restart the watch by holding down all 3 buttons together. Then, go to settings and turn on "Data Roaming". Make sure the APN setting is set to "1-first".
If you don't see APN in the watch settings, take out the SIM card, put it back, and restart the watch.
Above image shows no 4G sign shown as network is not detected.
Once watch is able to detect network, 4G sign will be shown on the watch main screen.
You may contact our customer support at support@myfirst.tech if the issue persists.