Troubleshooting

Common issues and solutions for Antigravity Claude Proxy

Common Issues

Windows: OAuth Port Error (EACCES)

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:

Option 1: Use a Custom Port (Recommended)

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.

Could not extract token from Antigravity

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

401 Authentication Errors

The token might have expired. Try refreshing:

curl -X POST http://localhost:8080/refresh-token

Or re-authenticate the account:

antigravity-claude-proxy accounts

Rate Limiting (429)

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)

Account Shows as Invalid

Re-authenticate the account:

antigravity-claude-proxy accounts
# Choose "Re-authenticate" for the invalid account

403 Permission Denied / VALIDATION_REQUIRED

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.