Automatically register user for course following payment


I might be overlooking a setting here, but when I tested the checkout workflow (Marketpress), the user was not automatically granted access to the course, requiring that I manually close out the order and then manually register the customer to the purchased course.

Is there a way to have users gain automatic registration following payment -- either via a setting (most preferable), adding a snippet to functions.php (also fine), or do I have to install another plugin (least preferable)?

Thanks for your help!