Android 'Authentication Required' Google Play — Fix Guide

What it means

'Authentication is required. You need to sign into your Google account' on the Play Store means the app store on your phone has lost its grip on your Google credentials.
You're still signed into Google for Gmail and other apps — only the Play Store's authentication has expired or got corrupted.
The usual cause is a stale token after a password change, a clock that's wrong, or a Play Services cache that needs clearing.
The fix doesn't normally need a factory reset or losing your apps.

Affected Models

All Android phones and tablets with Google Play
Common after changing your Google password elsewhere
Also seen after a long stretch of not opening the Play Store

Common Causes

Google account credentials cached by Play have expired
Account password recently changed on another device
Two-step verification turned on, and the Play Store's stored token isn't accepted any more
Phone's date and time wrong
Google Play Services or Google Services Framework cache corrupted
Account temporarily flagged by Google's security checks
Multiple Google accounts on the phone and the Play Store is using the wrong one

How to Fix It

Pull down to refresh the Play Store.

Open the Play Store, swipe down from the top of the screen.
Often the store re-authenticates silently and the error disappears.
Try opening an app's page; the message may be gone.
Restart the phone.

Hold the power button and choose Restart.
This clears the stuck authentication state and re-reads your Google account on next boot.
The error often clears on the first launch after restart.
Clear Play Store and Play Services cache.

Settings > Apps > Google Play Store > Storage > Clear cache.
Then Settings > Apps > Google Play Services > Storage > Clear cache.
You stay signed in.
If the error continues, go back and tap Clear storage / Clear data on Play Store (you don't lose installed apps; the store rebuilds its local index).
Fix the date and time.

Settings > System > Date & time > Set time automatically.
A wrong clock breaks the secure connection to Google and authentication silently fails.
Remove and re-add the Google account.

Settings > Accounts > Google > [your account] > Remove account.
Reboot.
Settings > Accounts > Add account > Google, sign in.
You'll be asked to approve a two-step prompt on another device, or to enter a code — finish that and the Play Store accepts the fresh token.
Pick the right account in the Play Store.

If you have more than one Google account on the phone, the Play Store may be trying to authenticate the wrong one.
Open Play Store, tap your profile photo top right, switch to the account you actually want.
Then try buying / installing / updating again.
Update Android and Play Services, then retry.

Settings > System > System update — install anything pending.
Play Store > profile > Manage apps & device > update Google Play Services.
If 'Authentication is required' keeps appearing after a fully updated phone, fresh sign-in, and correct clock, sign into your account at myaccount.google.com from a browser to check for security alerts — Google sometimes asks you to confirm a sign-in there, and clearing it makes the Play Store happy again.

Frequently Asked Questions

Will fixing the 'Authentication is required' error delete my Android apps?

No.
None of the steps that fix this error remove your installed apps.
Clearing the Play Store's cache or data only rebuilds its local index of which apps you have; the apps themselves and their data stay where they are.
Removing and re-adding your Google account signs you out of Google's services briefly but doesn't uninstall anything.
Even a factory reset — which you don't need for this — would restore your apps when you sign back into your Google account.
It's safe to follow the steps without worrying about losing apps.