Q: What does “Could not download page (407)” mean? A: A 407 error indicates that the proxy between your device and the internet requires valid authentication and the client did not provide acceptable credentials. It often appears as “Proxy Authentication Required” or “Could not download page (407)”, and you can usually fix 407 proxy authentication quickly by checking credentials and proxy settings. Q: What are the common causes of a 407 proxy authentication error? A: Common causes include wrong or expired username/password, an outdated proxy address or port, clock mismatches that break Kerberos/NTLM, cached bad credentials, a mismatched auth scheme (Basic vs NTLM/Kerberos), or VPN and firewall routing changes. These issues typically prevent the proxy from accepting the request. Q: What quick checks should I run first to fix a 407 error? A: Start by confirming your proxy username and password, verifying the proxy host and port, syncing your system time, and clearing saved logins in your browser or OS. Try an incognito/private window and run a quick curl test to see the raw error; these quick checks often solve the issue and help fix 407 proxy authentication. Q: How do I clear cached proxy credentials on Windows, macOS, and browsers? A: On Chrome/Edge clear cookies and cached images/files via Settings > Privacy > Clear browsing data, on Windows remove proxy entries from the Windows Credential Manager, and on macOS delete proxy items in Keychain Access. After clearing saved credentials, retry access so the proxy will prompt for fresh login details to help fix 407 proxy authentication. Q: How can I test whether the proxy is the cause of the 407 block? A: If policy allows, temporarily disable the proxy and load a test site; if it works, the network path is fine and the proxy is the issue. You can also run the curl example from the guide (curl -I -x http://user:pass@proxy:port https://example.com) to view the raw 407 response. Q: What should I do if my application supports only Basic auth but the proxy uses NTLM or Kerberos? A: If your app only supports Basic authentication and the proxy requires NTLM or Kerberos, the requests will fail until the auth methods match. Adjust the application to support a compatible method or ask IT to allow a compatible auth scheme so you can fix 407 proxy authentication. Q: Which environment variables matter for command-line tools to avoid 407 errors? A: Check and correct HTTP_PROXY, HTTPS_PROXY, http_proxy, https_proxy and NO_PROXY or no_proxy variables, and include credentials if required by your proxy. Ensuring these environment variables are accurate helps command-line tools authenticate through the proxy and avoid 407 responses. Q: How can I confirm that a 407 proxy authentication issue is fully resolved? A: Load a site that failed before without prompts, run curl with -v to ensure no 407 appears, and check your app logs for expected status codes like 200 OK. You can also ask a teammate to try the same settings to rule out device-specific problems and confirm you fixed 407 proxy authentication.