The FollowMee app works in the background and requires that background data is enabled. This setting is enabled by default when you install the app. If it is disabled, you can enable it by going to Settings -> Apps & Notifications -> FollowMee.
Select "Mobile data & Wi-Fi". Enable both "Background data" and "Unrestricted data usage". This app uses
very little data. Enabling "Unrestricted data usage" ensures that the app continues to track when "Data Saver" has been turned on.
Related
What Android settings and permissions are required for the app?
How do I enable location service in Android?
What permission does the Android app need?
How do I enable background data in Android?
What additional settings do I need to set for some Android models?