App can’t install is one of the most irritate error in android phone and table, the error could be (error code 505, error code 504, error code 503), sometime it happen because of google play store or play service, so before you do any hard work to fix this error, you should try this easy method to fix this problem, hope this will helps to fix your problem.
1. Go to phone “setting” than “Apps or app manager” open “google play services”
2. Tap on “Storage” than tap on “Clear cache”
3. Do the same to “Google play store”
4. If you are getting error to update any app, clear the app cache than try