Sorry, you don't need to watch this video.
I had this error on my chromebook when trying to log into the elementary website for orangeusd.org
it kept on saying: Http error 400. Bad Request - Request too Long.
Needless to say the usual troubleshooting didn't work: Close browser or restart laptop.
1) One possible solution is to "Clear Browser Data" in More Tools under the 3 vertical dots at the top right of the browser.
2) Alternatively, you can use the "FORCE REFRESH" which will force a refresh without using cached history:
ON PC: ctrl + refresh button with mouse click
On MAC: apple key + refresh button with mouse click.
Not sure if this video will help but for all those suffering parents like me... hopefully this might help you get your kid logged in.
Oh yeah.. this was happening with me trying to log into seesaw too! Seesaw is for assignments for my gradeschooler.