Error - Unable to add a collaborator

I added a collaborator on one website with no issues, but when I try to add them to another website, it is saying “Please enter the correct email.”

Hey, that means we have no user in Divhunt with that email. Your collaborator first needs to register on Divhunt, and then you can invite him.

It doesn’t make sense to me.

The screenshot shows she an existing collaborator in another website.

I should be able to easily add her to another website as a colloborator.