How to Fix iCloud Error 4016

iCloud error 4016 indicates that your iCloud sync session has expired or the authentication token is invalid. You’ll typically see “Sync failed. Your session has expired. Please sign in again (Error 4016).”

Step 1: What Causes iCloud Error 4016

• Extended period of inactivity causing the session token to expire
• Password change on your Apple ID that invalidated existing sessions
• Incorrect system date or time causing token validation to fail
• Multiple simultaneous sign-ins triggering a security reset
• Corrupted Keychain entry storing an outdated authentication token

Step 2: Re-authenticate Your iCloud Account

On macOS:

1. Open System Settings > Apple ID and click Sign Out
2. Choose whether to keep a copy of your iCloud data on this Mac
3. Restart your Mac, then sign back in at System Settings > Apple ID

On Windows:

1. Open iCloud for Windows and click Sign Out
2. Restart your computer and sign back in
3. Select the services you want to sync and click Apply

Step 3: Clear Expired Sync Tokens

On macOS:

1. Open Keychain Access from Applications > Utilities
2. Search for iCloud and delete entries named iCloud Identity or iCloud Auth Token

# Clear cached sync state files
rm -rf ~/Library/Application\ Support/CloudDocs/session
killall bird && killall cloudd

3. Restart your Mac and sign back into iCloud when prompted

Step 4: Fix Date and Time Configuration Issues

Authentication tokens are time-sensitive — a wrong system clock makes tokens appear expired.

On macOS:

1. Open System Settings > General > Date & Time
2. Enable Set date and time automatically

# Verify system time against network time
sntp time.apple.com

On Windows:

1. Right-click the clock in the taskbar > Adjust date/time
2. Toggle on Set time automatically and click Sync now

w32tm /resync /force

If the time difference exceeds 5 minutes, token validation will fail.

winget uninstall "iCloud"
winget install --id Apple.iCloud