1. Avoid logging in between 10pm and 12am. The system is often busy during this time and is more likely to result in an error.
2. Try a different internet connection: The issue may involve an unstable WiFi connection. Please switch to a different WiFi source (or 4G/3G) and try logging in.
3. Try a VPN: The issue may have to do with the region from which you are trying to connect to the app. Please connect to a VPN and try again.
Search for "VPN" on the App Store / Google Play store to find one.