Team Project Invite Error

Hello,

CC user here and looking to start collabing with my collegue for out projects. During the invitation process his email doesn't seem to be able to accept invitation from other projects. I am able to accept an invitaiton when he is the owner.  I am also able to invite other users.  Just this one paticular user that can't seem to accept an invite.  I enter in his email (also has paid suscription and updated software) it finds it but then as the actual invite sends if simply fails with no explaination.  Just a big nope.  I tried calling customer service but they really could figure out the issue either. Here are some stills for referece:

Again. It's only Ivan here that can't accept. Other user invited work.