I have an existing API Role that has associated API Users to it, but once I fill in the new user information and get to the Send button and receive the code T"he pop-up says, "An invitation is not required for API only," but that doesn't mean you've done something wrong. It just means we'll create the role without an invite email having to be sent" But then the SEND button closes out and nothing happens / user is not created.
There might be a bug. I just created an API role and API user recently without a problem.
So you might want to check with Marketo support.
Pls provide some screenshot.
And remember that creating the API user is not enough. You then need to go to the admin -> Launchpoint and create a custom service there to get the credentials.