can't add collaborator - incorrectly says he doesn't have an account

Another developer made a github account today so that I could add him as a collaborator.  When I try to add him as a collaborator, it won’t let me while telling me he doesn’t have an account.  We verified that the email for the account was correct, but it still says he doesn’t exist.  I’ve refreshed that page a number of times. Does it take a long time for new accounts to be recognized, or is there another problem?

Hi,

The user you are inviting must have their email address listed publicly. If their email address is not public the API cannot lookup the user by that email even if they have it in their account privately. You can always add users by their GitHub account name if the email address doesn’t work.

More details please refer to below link:

https://github.com/isaacs/github/issues/491