HTTP 407 means the proxy did not accept the authentication supplied for the request.

Steps

1. Confirm that the username, password, host, and port all belong to the same active product.
2. Remove accidental spaces and verify special-character encoding.
3. If using IP whitelist authentication, confirm the current public outbound IP is approved.
4. Test with curl to separate application configuration from account configuration.
5. Regenerate credentials if exposure or corruption is suspected.

For account-specific values, use the endpoint, port, credentials, and location shown in your MaskProxy dashboard. Do not publish proxy credentials in screenshots, tickets, or public code repositories.