It's normal for the GPS to show as OFFLINE when it has been stationary for 10 mins or more.

If you think there is an issue with the GPS or would just like to check it is working send an SMS to the GPS saying - Check123456 - the GPS should respond with the below image and the device will then show on the app as "moving" or "stop".

If the device doesn't respond the battery could have run-out, there maybe no mobile coverage or an issue with the     SimCard. It's worth retrieving the GPS and charging it up and checking the SimCard is working correctly.

GPS offline check