Have you tried clearing the cache of Google Play Store and Google Play Services?
If that doesn't work, then the next step is to clear the data from these two apps, open the Play Store, then wait five minutes or so and try again.
The wait is for Google to update the data in those apps.
If it still won't work, or won't update, then clear the data again and open the Play Store.
Goto:
Hamburger menu
Settings
Play store version
Tap Play store version to download the latest version of the Play Store.
Wait a few for the update to come to Play Services, and then try again.