Proxy Authentication Failed: How to Fix Username, Password and Whitelist Problems

Symptoms you usually see

• Browser keeps asking for proxy username and password.
• Script returns 407, authentication failed or connection unauthorized.
• The same proxy works from one server but not another.
• The proxy works without auth only after whitelisting the machine IP.

Most likely causes

Fix workflow

An online Proxy Tester sends requests from its own server. Its success does not confirm authentication from your computer, VPS or application. For IP authorization, use the public outgoing IP of the machine making the request. Follow the working-proxy guide to compare a direct connection, a request through the proxy and the application from the same device.

1. Test one request through the proxy from the device or server running the failing application, outside that application.
2. Rebuild the proxy string using the Proxy Formatter.
3. Confirm whether the provider expects username/password or IP authentication.
4. If IP auth is enabled, check the public IP of the device or server making the request.
5. Retry in the original application only after the same-device proxy request works.

Field notes

Proxy errors become harder to solve when every layer changes at the same time. Keep the proxy, target URL, protocol and client constant until you know which layer fails. If the proxy fails in a simple direct test, the browser or script is not the first thing to fix. If the proxy works in a direct test but fails in the application, focus on application format, authentication handling, DNS behavior and whether another proxy/VPN setting overrides the request.

When debugging production jobs, save the exact proxy format, source machine, public IP, target URL, response code and timestamp. That small record is often enough to separate a temporary route failure from a repeated configuration mistake.

Example debugging sequence

Start with one proxy and one target URL. From the affected machine, check that the target responds without the proxy, then test that target through the proxy with the same protocol, authentication method and timeout. Compare the result with the failing application. An online tester result comes from a different source machine and cannot validate your machine's whitelist entry. If the same-device proxy request fails, inspect host, port, protocol, credentials and source-IP authorization. If it works but the application fails, check that application's proxy format and settings. Change one relevant variable at a time and keep credentials private.

For teams, write the final working format into a short runbook. The next person should not need to rediscover whether the tool expects host:port:user:pass, a full proxy URL or separate username and password fields.

What should I update after changing proxy credentials?

For a BuyProxies service, sign in to the client area and open the intended service. Its Access section shows the Username, Password and Proxy type; Change credentials is the separate account control.

1. After completing a credential change, reopen the service details and check the current values privately.
2. Update any application profile, secret store or imported list that still contains the previous username and password. Check the host, port and protocol against the current service details too.
3. Run one controlled request from the affected device before restarting the full workflow.

Do not assume a saved application profile updates when you change the service credentials. Proxy credentials and the destination website’s login are separate; keep both out of screenshots, public logs and shared examples.

FAQ