There are two methods for adding a customer to subcription payments.
1) Go to Payments > Subsriptions
Subscription Plan Payments
You can create subscription plans for your business and enroll customers into them.
1) From the Subscriptions Page, click on the Manage Plan button
2) From the Mange Plan pop up, click on the Create Plan button
3) Enter plan details in the Add Plan pop up and click Save Plan.
Individual Recurring Payments
You can create subscribe customers individually to unique, recurring payment plans.
1) Open the Contact and click on the Subscriptions Tab and click on the Add Subscription Button
2) In the Manage Subscription Pop Up, enter details and Save Susbcription.