Skip to main content

​
Common Issues

On Windows, the default OAuth callback port (51121) may be reserved by Hyper-V, WSL2, or Docker. If you see:
Error: listen EACCES: permission denied 0.0.0.0:51121
The proxy will automatically try fallback ports (51122-51126). If all ports fail, try these solutions:Set a custom port outside the reserved range:
# Windows PowerShell
$env:OAUTH_CALLBACK_PORT = "3456"
antigravity-claude-proxy start

# Windows CMD
set OAUTH_CALLBACK_PORT=3456
antigravity-claude-proxy start

# Or add to your .env file
OAUTH_CALLBACK_PORT=3456

​
Option 2: Reset Windows NAT

Run as Administrator:
net stop winnat
net start winnat

​
Option 3: Check Reserved Ports

See which ports are reserved:
netsh interface ipv4 show excludedportrange protocol=tcp
If 51121 is in a reserved range, use Option 1 with a port outside those ranges.

​
Option 4: Permanently Exclude Port (Admin)

Reserve the port before Hyper-V claims it (run as Administrator):
netsh int ipv4 add excludedportrange protocol=tcp startport=51121 numberofports=1
The server automatically tries fallback ports (51122-51126) if the primary port fails.
If using single-account mode with Antigravity:
  1. Make sure Antigravity app is installed and running
  2. Ensure you’re logged in to Antigravity
Or add accounts via OAuth instead:
antigravity-claude-proxy accounts add
The token might have expired. Try refreshing:
curl -X POST http://localhost:8080/refresh-token
Or re-authenticate the account:
antigravity-claude-proxy accounts
With multiple accounts, the proxy automatically switches to the next available account. With a single account, you’ll need to wait for the rate limit to reset.The proxy uses smart account selection strategies to minimize rate limiting:
  • Sticky: Stays on same account (best for caching)
  • Round-Robin: Rotates every request (best for throughput)
  • Hybrid: Smart distribution based on health and quotas (default)
Re-authenticate the account:
antigravity-claude-proxy accounts
# Choose "Re-authenticate" for the invalid account
If you see:
403 VALIDATION_REQUIRED - Account requires verification
This means Google requires your account to complete verification (phone number, captcha, or terms acceptance).The proxy handles this automatically:
  1. The affected account is marked invalid and the proxy rotates to the next available account
  2. If a verification URL is provided by Google, it’s stored and shown in the WebUI
  3. Other accounts continue working normally while the affected account is paused
To fix the affected account:
  1. Open the WebUI at http://localhost:8080
  2. Find the account marked with an error badge
  3. Click the FIX button - this opens the Google verification page directly
  4. Complete the verification (phone number, captcha, etc.)
  5. Click the ↻ Refresh button on the account to re-enable it
If the FIX button opens an OAuth page instead (no verification URL was provided), re-authenticate the account:
antigravity-claude-proxy accounts
# Choose "Re-authenticate" for the invalid account
If all accounts are invalid, the proxy returns an error immediately instead of waiting indefinitely:
All accounts are invalid: Account requires verification. Visit the WebUI to fix them.
Verification errors persist across server restarts until resolved. Auth errors (token revoked/expired) are reset on restart and require OAuth re-authentication via the FIX button.

Build docs developers (and LLMs) love

Get started for freeTalk to us