macOS App Store Error 400 — What It Means & How to Fix It

What Does This Error Mean?

App Store Error 400 on Mac means the App Store received a bad request — usually because your Apple ID session is invalid or expired. This error commonly appears when trying to download, update, or purchase an app. It is rarely a problem with your Mac itself. Signing out and back into your Apple ID almost always fixes it.

Affected Models

MacBook Air (all models)
MacBook Pro (all models)
iMac (all models)
Mac mini (all models)
Mac Pro (all models)

Common Causes

Apple ID session has expired or become invalid and needs to be renewed
Apple ID server-side issue temporarily affecting authentication
Incorrect date and time on your Mac causing session token validation to fail
Corrupted App Store cache files causing bad requests to be sent
Two-factor authentication prompt not being completed properly

How to Fix It

Sign out of the App Store. Open the App Store, click your name or profile picture at the bottom of the sidebar, and click Sign Out. Wait 30 seconds, then sign back in with your Apple ID.

This is the single most effective fix for Error 400. A fresh sign-in generates a new valid session token.
Check your Mac's date and time. Go to System Preferences (or System Settings) > Date & Time. Make sure 'Set date and time automatically' is enabled.

An incorrect system clock causes Apple's authentication system to reject the session as invalid, producing a 400 error.
Clear the App Store cache. Open Terminal and type: open '$TMPDIR../C/com.apple.appstore' and delete the files inside. Also delete the folder at: ~/Library/Caches/com.apple.appstore/

Corrupted cache files can cause malformed requests. Deleting them forces the App Store to rebuild clean cache data.
Check Apple's System Status page at apple.com/support/systemstatus. If the App Store or Apple ID services show a yellow or red indicator, Apple is experiencing a service issue and the error is on their end.

Apple service outages usually resolve within a few hours.
If the error persists after signing out, clearing cache, and verifying the time, restart your Mac and try again. A macOS restart clears temporary network sessions and system state that can cause persistent 400 errors.

After restarting, open the App Store, sign in, and try your download or update again.

When to Call a Professional

App Store Error 400 does not require professional help. Sign out and back into your Apple ID, clear the App Store cache, and make sure your system clock is correct. Apple Support is available at support.apple.com or by phone at 1-800-APL-CARE.

Frequently Asked Questions

What does a 400 error mean in general?

In web and network terms, a 400 error means 'Bad Request' — the server received a request it did not understand or that was malformed. In the App Store context, it usually means your authentication session sent an invalid or expired token. It is a client-side session issue, not a server failure.

Will I lose my purchased apps if I sign out?

No. Your purchased apps are permanently linked to your Apple ID, not to the installation on your Mac. Signing out and back in does not affect any apps already installed. All your purchased and downloaded apps remain accessible.

Does Error 400 affect iPhone purchases too?

App Store errors on Mac and iPhone are separate sessions. A session issue on your Mac does not affect App Store purchases on your iPhone. However, if your Apple ID itself has a problem, you may see errors on both devices.