Q: What does a 401 Unauthorized status mean? A: A 401 Unauthorized means the server requires authentication and did not accept your credentials. Common triggers include expired sessions, wrong URLs, or a missing Authorization header, and following the five-step checklist will help fix 401 unauthorized error. Q: What should I check first to fix a 401 Unauthorized? A: Start by verifying the full URL, path, trailing slashes and environment to confirm you are on the correct domain. Log out and log in again, reset your password if unsure, and confirm account status and any MFA prompts to fix 401 unauthorized error. Q: How can cookies and cached credentials cause a 401 and what should I do? A: Stale cookies and cached credentials can block new logins and produce a 401. Clear cookies and site data, try an incognito window, disable extensions that modify requests, and ensure your device clock is correct to fix 401 unauthorized error. Q: Why does an API return 401 and how do I resolve it? A: APIs often return 401 when tokens expire or required headers are missing; include the Authorization header (for example Authorization: Bearer YOUR_TOKEN) and refresh access tokens using the refresh token flow. Check token expiry and scopes, use the correct base URL and sync clocks to fix 401 unauthorized error. Q: Can reverse proxies or server rules cause 401 responses? A: Yes, reverse proxies and middleware can strip or block Authorization headers and cause 401 responses; forward Authorization explicitly (for NGINX use proxy_set_header Authorization $http_authorization;) and review .htaccess or Basic Auth settings. Also check IP allowlists, rate limits, and that protected endpoints still accept valid tokens to fix 401 unauthorized error. Q: How should I test and collect evidence when troubleshooting a 401? A: Use curl, Postman, or HTTPie to make minimal requests with the required header or cookie and compare a working call to a failing one to see what differs. Inspect response headers and server logs, and collect timestamps, URLs, request IDs and sample curl commands when contacting support to help fix 401 unauthorized error. Q: What quick steps can I try before doing deep troubleshooting? A: Quick wins include reloading the page after logging in, resetting your password and signing in fresh, or using an incognito window. Turning off VPNs, proxies and extensions and pasting a fresh API token are simple measures that often fix 401 unauthorized error. Q: How can I prevent 401 Unauthorized errors in the future? A: Prevent future 401s by using a password manager, enabling MFA, and automating token refresh well before expiry. Monitor rate limits and auth failure spikes, ensure proxies forward Authorization consistently, and document environments and rotate keys on a schedule to reduce incidents where you must fix 401 unauthorized error.