Authentication is Required Google Play Store I have tried everything that was said in the answers below but it just won't work. I want to download an application but whenever I accept the permissions prompt,  a notification appears: "Authentication is required. Please sign into your Google Account."

I don't know what to do anymore. Can anyone please help me?
Delete your Play Services data. 

Go to Settings, Storage, Applictions, and look for Google Play Services. Delete data. Then, go back and scroll until the All tab. Look for Google Play Store. Delete data. Reboot. Enter credentials. Try again.