So I’m guessing this question is going to be more about the “wording”. What specifically is involved with your definition of “double opt in”. I’m putting it this way because the api cannot do this and because you are yielding the results of unmarketable. The api can only single optin an email address that is not opted out. A double optin must be triggered through a link via an email.
Here is the api docs for doing that:
https://developer.infusionsoft.com/docs/xml-rpc/#email-opt-in-an-email-address