installation app blocked by play protect
I found the solution: Go to the link below and submit your application.
Play Protect Appeals Submission Form
After a few days, the problem will be fixed
Try to create a new key store and replace with old one, then rebuild a new signed APK.
Update: Note that if you're using a http connection with server ,you should use SSL.
Take a look at: https://developer.android.com/distribute/best-practices/develop/understand-play-policies