What is this and how do I fix it on my Mac Book using Safari?
400 Bad Request Request Header Or Cookie Too Large
rdwr
MacBook Air 13″, macOS 13.5
In addition to MrHoffman's suggestions that particular HTTP status message can also be caused by some Safari Extension (such as an ad-blocker) on some websites.
Review If Safari doesn't open a page or work as expected on your Mac - Apple Support for some suggestions. Some of them are overly broad, but others may help isolate the cause.
That’s a HTTP status, which usually involves a website and a browser, or sometimes an app that is using HTTPS to connect to a remote server. Might also arise within the context of a web server, too.
If you have any add-on anti-malware apps or any add-on first-few-hops VPN clients or add-on cleaner apps installed, remove all that per the vendors’ instructions, restart macOS, and test again. Those sorts of apps can insinuate themselves into network activity, and in potentially unexpected ways.
If you’re not maintaining the web server and web browser or some other app you’re using, and not adding anti-malware or VPN client apps unto the mix, contact whoever is supporting the web server you are accessing, or the app you are using.
400 Request
