There are two ways that a customer can enroll in AutoPay. The first, which you are most likely familiar with, is from an invitation that you send them from the Business Portal. This sends the customer an email inviting them to enroll in AutoPay.
The second way a customer can enroll in AutoPay is directly through their user dashboard. If they log into Plastiq and edit their recipients, they do have the ability to enroll in AutoPay if your business account is activated for AutoPay. Once they enroll, their enrollment will appear in your Pending Enrollments screen, just like all other AutoPay enrollments.
If you do not want to approve AutoPay for a particular customer, you can deny their enrollment. This will send them an email notification to let them know that AutoPay has been declined by the business and that they will still need to submit their payments directly.