Bulk add subscribers to forms

Adding subscribers to double opt-in forms will trigger sending an Incentive Email. Subscribers already added to the specified form will not receive the Incentive Email again. For more information about double opt-in see "Double opt-in". <br/><br/>The subscribers being added to the form must already exist. Subscribers can be created in bulk using the "Bulk create subscriber" endpoint.<br/><br/>See "Bulk & async processing" for more information.