We kindly suggest to do the following steps:
-Make sure you have Android 5.0 or above;
-Force Close the app;
- Go to Settings, Apps and select Clear Data for your game (don't worry, you won't lose your game progress);
- Under your phone's Settings, the Unknown sources option is checked as enabled. This will allow you to install third-party .apk files on your device;
-Uninstall the app and reinstall the app;
-Restart your phone;