I don’t understand why the official app isn’t working properly; I imagine it’s because of the Android version or the phone, but it works perfectly on iPhone.
It should work on Android as well, but often the default aggressive energy saving settings are too strict.
I’d ask support for guiding & hints.
In order to use Fake GPS:
Open the Settings app on your Android-powered device.
Tap About Phone or About Tablet.
Find the Build Number. On some devices, you may need to tap Android Version or Software Information to find the Build Number.
Tap the Build Number seven times in quick succession. You’ll see an on-screen countdown indicating how many more taps are needed.
Once you’ve tapped it enough times, you’ll see a confirmation message.
Accessing the Developer Options menu:
After enabling developer mode, a new Developer Options menu will appear in your device’s settings;
It’s usually located in the main settings menu or under System
In the developer options screen, you’ll be able to enable/disable Fake GPS app at the “Location” entry: