I have sent an invite for someone to use my Final Draft 13 site license, they have accepted the invite, but they can't sign into Final Draft 13

On rare occasions, a user has received the invite to use Final Draft 13, accepted the invite, set up an account, downloaded and installed Final Draft 13, and the user still cannot sign in to Final Draft 13.  Please contact licensing@finaldraft.com to troubleshoot this issue.