Why your proxies suddenly return 407

407 Proxy Authentication Required means the proxy received your request and refused it because the credentials were wrong or missing. In practice there are only a few causes.

You changed the authentication mode

This is the usual one. Switching a batch between user/pass, IP whitelist and SOCKS5 regenerates the credentials for every address in that batch. The old username and password stop working immediately.

The fix: regenerate your list from the dashboard and update whatever holds the old values.

You are on IP whitelist and your address changed

Under IP whitelist authentication there is no username or password — the proxy decides based on where the connection came from. If your public IP changed, you are no longer on the list.

The fix: check your current public address and update the whitelist.

Your tool is sending credentials in the wrong shape

Some tools expect user:pass@host:port and others expect host:port:user:pass. Sending one where the other is expected usually produces a 407 rather than a helpful error.

The fix: use the format selector when you generate the list rather than reformatting by hand.

It is not a 407 at all

If the connection is refused outright, or times out, that is a different problem — usually an exhausted bandwidth allowance or an expired term. Check the plan page.