icloud Code 4020

How to Fix iCloud Error 4020

Diagnostic Procedures

  • 1 What Causes iCloud Error 4020
  • 2 Test and Improve Your Network Connection
  • 3 Configure Firewall and Proxy Settings
  • 4 Reset iCloud Network Services
  • 5 Monitor and Retry Stalled Transfers

How to Fix iCloud Error 4020

iCloud error 4020 occurs when a file transfer times out due to a network interruption. You may see “Connection timed out. Unable to complete the file transfer (Error 4020).”

Step 1: What Causes iCloud Error 4020

  • Slow or unstable internet connection with high latency or packet loss
  • Firewall or security software blocking Apple’s content delivery endpoints
  • Corporate proxy servers interfering with long-lived HTTPS connections
  • ISP throttling of cloud storage traffic during peak hours
  • Wi-Fi signal issues causing intermittent disconnections

Step 2: Test and Improve Your Network Connection

  1. Run a speed test at https://www.speedtest.net — you need at least 2 Mbps upload and 5 Mbps download
  2. Connect via Ethernet cable for the most reliable connection
  3. Disconnect bandwidth-heavy devices and restart your router
# Test connectivity to Apple's iCloud servers (macOS)
ping -c 10 gateway.icloud.com
nslookup p33-content.icloud.com
:: Test connectivity on Windows
ping gateway.icloud.com -n 10
tracert gateway.icloud.com

Step 3: Configure Firewall and Proxy Settings

On macOS:

  1. Open System Settings > Network > Firewall > Options
  2. Ensure iCloud services are set to Allow incoming connections
  3. For third-party firewalls (Little Snitch, Lulu), allow *.icloud.com and *.apple.com on port 443

On Windows:

  1. Open Windows Security > Firewall & network protection > Allow an app through firewall
  2. Ensure iCloud, iCloudDrive, and iCloudPhotos are checked for both Private and Public
netsh advfirewall firewall add rule name="iCloud" dir=in action=allow program="C:\Program Files (x86)\Common Files\Apple\Internet Services\iCloudServices.exe"

If behind a corporate proxy, whitelist *.icloud.com and *.apple.com domains.

Step 4: Reset iCloud Network Services

On macOS:

killall bird && killall cloudd && killall nsurlsessiond
sudo ifconfig en0 down && sudo ifconfig en0 up

Test in Safe Mode (hold Shift on Intel, or hold Power then select Safe Mode on Apple Silicon) to rule out third-party interference.

On Windows:

netsh winsock reset
netsh int ip reset
ipconfig /release && ipconfig /renew && ipconfig /flushdns

Restart your computer and reopen iCloud for Windows.

Step 5: Monitor and Retry Stalled Transfers

On macOS:

  1. Open Activity Monitor > Network tab and look for bird or cloudd processes
  2. If bytes are not increasing, the transfer is stalled
brctl monitor com.apple.CloudDocs
  1. Remove the stuck file from iCloud Drive and re-add it to force a retry

General tips:

  • Transfer files one at a time rather than in large batches
  • Keep your device awake and plugged in during large transfers
  • Compress files into .zip archives — they often transfer more reliably

Tip: If error 4020 recurs with a specific file, try uploading it via https://www.icloud.com/iclouddrive instead of the desktop client.