Save a new subscriber to a Paubox Marketing Subscription List
This will create a new subscriber on a Paubox Marketing Subscription List when using the form_id attached to the subscription list. This will not update existing subscribers or add any new custom fields. Custom fields must be setup in Paubox Marketing in order for posted data to be saved. It does not provide validation. The form_id is unique to this subscription list.
Code: 404, Subscription list with provided form_id cannot be found
Code: 422, Subscriber already exists / Other error.