[coocooc]

Authorization code mismatch. Are you accessing this function correctly? Please go back and try again.

Using Firefox 119.0.1 in Ubuntu, I cannot login to this site, getting the above error message. A related Reddit post suggested to use Firefox's private mode, and this actually works (writing in private mode this very moment).
There is uBlock origin installed, but it shows zero blocked elements and disabling uBlock also does not allow the login here.

What could be the culprit?

[DarrenHill]

A bad cookie or something like that, or some other plugin that's getting in the way and screwing things up.

The former is the simplest one to try by clearing the site cookie in your browser.
If not that, then look at whatever else you may have installed in FF which could be affecting things, but that private mode disables.

[coocooc]

OK, deleting the cookies for kodi.tv worked, I can login outside private mode again.

Thanks for the quick hint! :-)

[DarrenHill]

Thread marked solved.