What common errors usually mean and what to try first.
407 Proxy Authentication Required
The proxy rejected you — not the website.
- Wrong username or password, or wrong auth format for this provider.
- Special characters in the password must be URL-encoded (
@→%40,:→%3A). - Using IP allowlisting instead? Your current public IP must be on the allowlist.
403 Forbidden (from the site)
The target blocked the request.
- IP reputation: move up a tier (datacenter → residential/ISP → mobile).
- Fingerprint: realistic headers, consistent User-Agent, and a real browser for JavaScript-heavy sites.
- Some providers block certain domains for compliance — check their restricted-targets list.
429 Too Many Requests
You're rate-limited. Slow down, rotate IPs more often, and add exponential backoff.
502 Bad Gateway / 504 Gateway Timeout
The proxy couldn't get a good answer from upstream. On residential networks that often means the peer dropped. Retry with a new IP or session.
503 Service Unavailable
The proxy is overloaded, the target is down, or there are no IPs available for your geo-targeting. Widen the targeting (country instead of city) and retry.
ERR_TUNNEL_CONNECTION_FAILED / "Tunnel connection failed"
The HTTPS CONNECT request was refused — usually bad auth, a blocked target domain, or an exhausted plan.
SSL / "wrong version number" errors
Usually https:// at the start of the proxy URL when the proxy expects plain http://. Most proxy endpoints use http://HOST:PORT even for HTTPS websites.
Timeouts
Residential and mobile routes are slower than datacenter ones. Use 30–60 second timeouts, retry on a fresh IP, and track success rate per provider so you can compare.
Seeing an error that isn't listed? Check the provider's documentation for its own error codes.