Did you try this in another browser? clear cache/cookies? Usually these errors are the result of something being cached in the browser that wasnt supposed to be which causes issues submitting forms. sometimes misconfigured adblockers or javascript controlling extensions can do it too. ie inadvertantly blocking things needed for site functionality like this.
I did initially try this on two different browsers, Firefox & Librewolf (with uBlock) and it didn't work. After reading your comment, I downloaded ungoogled Chromium, didn't install any addons or change any settings and it worked. Thank you!