Proxy Error Codes Explained: 407, 502, 503 in 2026

By Elena Park 2026-05-29 6 min read Engineering

407, 502, 503, 429 — proxy errors all look alike until you know what each actually means. Here's the cheat sheet.

407 Proxy Authentication Required

Your credentials are missing or wrong. Check Proxy-Authorization header or URL encoding (special characters in passwords need URL-encoding).

502 Bad Gateway

The proxy reached your target but got an error response or upstream IP failed. Retry with a new IP; if persistent, the target is down or blocking your provider's range.

503 Service Unavailable

The proxy itself is overloaded or your account is throttled. Wait and retry; if persistent, contact support — your plan may be over-quota.

429 Too Many Requests

Either the proxy or the target is rate-limiting you. Reduce concurrency, add jitter, or rotate IPs more aggressively.

403 Forbidden

The target identified you as a bot. Switch IP type (datacenter → residential), upgrade browser fingerprinting, or move to a managed Web Unlocker.

Read more on ToptierProxy Blog or see our Best Proxies 2026 guide.