If you go to the self-check portion of the app and the item “UnifiedNlp is registered in system” is unchecked, then the network location provider service of the app has not bound to the system and thus can't be used. There are two common reasons for this:
- You just installed microG/UnifiedNlp and have not rebooted
- You are running Android 7.0 (Nougat) or newer and installed microG/UnifiedNlp as a user app
First of all, the network location provider included in microG or the standalone UnifiedNlp requires a reboot to bind the provider to the system.
There was also a change in Android 7.0 that prevents user apps from being network location providers. Some ROMs have patched this out - usually the same ones that are patched for signature spoofing in the first place - but others have not. In order to use the location provider portion of microG or UnifiedNlp on these systems, the app needs to be installed as a system app. You can find flashable zips to install microG as a system app in the downloads section.
If neither of these are the problem, make sure you have at least one location provider backend installed.
For more information, see the setup guide.