solution for the time being:
the invite username is saved in the browsers local storage.
while on the 4player chess page, open chrome's developer tools -> application tab -> local storage and delete the "inviteUsername" entry.
https://stackoverflow.com/questions/9404813/how-to-view-or-edit-localstorage
Hi I have this problem with 4 player chess teams matchup in Chrome on a Mac. I use another premium account where I am able to invite teammates; however, if I log off from that account and log onto this one, there is still a username in the "Invite teammate" box, remembered from my premium account, and it is un-editable. Therefore I can't delete the name to try to find a matchup with a random partner and cannot at all play on this account in this browser...if I try to click ok it just thinks I am trying to invite that person and that I need a premium account. Kind of annoying to need to use a different browser like Firefox for a second account, and there's some small issues I have in non-Chrome anyway. Thanks for adding this to the list and keep up the good work.