The link to add a developer gives a 400 error

I tried to add a developer to an anymod project I created but received a 400 error. Is the link broken or does adding a developer require an upgrade?

Hi and welcome! It does not appear to be down, and you should be able to invite someone as a developer. There is a chance you had not confirmed your email address yet, in which case your invite would fail.

Can you try again? If it’s still not working we will look deeper.