its been a month and I still can’t join a cc from my iPad. I’m getting an invitation [...] and I get the oops message.
Get the owner's consent to apply to the CC yourself - he should then accept it, and hopefully, it will work.
Any fixes coming?
Problems with the owner's invitation have been reported a while ago. I heard of a fix and of continuing problems. In general, fixes may take some time - "soon" extends to eternity ;)