Error 504 in the Google Play store is generally associated with weak WiFi connections or mobile data networks, Google play store connection timed out. So the most common and easiest way to apply is to put your Android devices in Airplane mode, and then turn it off.

Regards,
Will

Try to follow the below methods to get rid of Error 504:

1. Clear App Data
- Go to Settings>> Application Manager or Apps>> Open “All” apps
- From the list of apps find Google Play store >>Clear Data and Clear Cache
- From the list of apps find Google Service Framework >> Clear Data and Clear Cache
- Now install or update the app from Google Play Store

2. Try Removing and Adding Gmail
- Go to system settings>> Accounts>>Google>>remove your Gmail account
- Now from settings>>Apps>>All> Force stop, Clear data and cache for Google Play Store, Google Service Framework and Download Manager
- Now again go to settings>> Accounts>>Google>>Add your Gmail account
- Restart your android and then accept all the Google terms and setup Google settings
- Rerun the Google Play Store and update or install your app.

Greetings,
Jimmy Wick