When a GSM device turns offline, please follow the instructions below to troubleshoot.
When the communication of your carrier network malfunctions, GSM device will turn offline until your carrier resumes the network. Additionally, please don’t place your GSM device in a place with weak signal or obstruction (inside metal box).
Try another place.
Check if the data plan for the SIM card is used up or has expired. Try a different SIM card which has enough data.