Double Opt-In (DOI) is currently not available with this module, as the status is hardcoded to subscribed.

As DOI is necessary for countries like Austria, Germany, Greece, Switzerland, Luxembourg and Norway this should be configurable for MC. To be more flexible, I would suggest setting the status to either one of these supported types (see MC API docs):

• pending This is the necessary status for DOI
• subscribed
• unsubscribed
• cleaned
• transactional

To leave this decision to the user, a new config option, f. ex. memberStatus could be introduced with a default value being subscribed.

I tested this: when setting pending as the status, the email is not directly added to the audience but instead you receive a DOI email, if you really want to subscribe.

I would create a PR, if that helps :)