I don't know what incognito is and I only have one device and I use Firefox, no other browser. I never had an issue like this before. It just started the day before I created this post. It worked, then it didn't. Now nothing seems to resolve the issue.

Also, just an FYI: I have always used the same browser and computer.

@Sioux1055

Great question, incognito mode, also called private browsing, is a setting on a web browser that prevents your browsing history, cookies, and other site data from being saved on your device, essentially making your internet activity invisible to other users on the same device, but not necessarily to websites or your internet service provider; it allows you to browse the web more privately on your own computer.   https://www.xfinity.com/support/articles/private-browsing

  A "400 Bad Request Request Header or Cookie Too Large" error means that the information sent by your browser to a website in the request header (like cookies) exceeds the server's allowed size limit, preventing the website from processing the request properly; essentially, you're trying to send too much data in the cookie section of your web request. 

• How to fix:

• • Clear cookies and cache: Often, the simplest solution is to clear your browser's cookies and cache, as outdated or excessive cookies can cause this issue. 

• • Check website logins: If you're logged into multiple websites with many cookies, try logging out of some to reduce the size of the cookie data. 

• • Contact website administrator: If clearing cookies doesn't help, the issue might be with the website's server settings, so contact the website administrator. 

You will want to try a different browser such as Google Chrome as well to see if the issue is with that specific browser