1. Make sure that you have GWENT installed from Play Store. If you see the "Your device is incompatible with this version" notification on Google Play GWENT page, your Android device is not supported.
2. Make sure your Android version is up to date, here's how: support.google.com/android/answer/7680439?hl=en
3. Try updating GWENT, Google Play Services and Google Play Store, here's how: support.google.com/googleplay/answer/113412?hl=en
4. Clear cache and data of GWENT:
5. Clear cache and data of Google Play Services & Store in the device's Settings app. Refer to the steps 2 & 3 here: https://support.google.com/googleplay/answer/9037938?hl=en
6. Change Wi-Fi to cellular, or the other way round. If you use Wi-Fi make sure nothing is interfering e.g. downloads/uploads, streams, other users. Avoid using VPN if possible.
7. Restart your device.
8. Try uninstalling and re-installing the game.