There are two key reasons why this occurs.
1. Your location function on your device is turned off
2. You are inside
If you are inside, go outside. The app needs a GPS position to be picked up before it begins or if you haven’t used the app for a while. Usually the issue is because people are indoors.
If you are outdoors move to another location to see if it helps the GPS system pick you up
If your location function is off check out this article [Link] where we run through how to check and enable for popular devices.