Hello, welcome in the forum and thank you for your purchase !
Sadly this app doesn’t work for me neither. I suspect this app needs a certification (SafetyNet) only available when the Google Play Services are installed.
MicroG was able to bypass until summer 2019 but Google changed something in the way SafetyNet works and MicroG isn’t able to bypass it anymore.
It’s the same problem with Snapchat for instance, you can’t login.
Nothing, if a user asks for it (in the settings of Apps) the app is added, there is no quality control.
You could add your app into this list of non-working apps.
Regards,
Anonyme.