On your PayFast account, do the following:

1. Log in to your PayFast account and navigate to Settings > Recurring Billing.
2. Click Enable or Edit next to Recurring Billing and enable Ad Hoc payments. (Once setup, WHMCS subscriptions will be found under Ad Hoc Agreements on your PayFast Dashboard.)
3. Ensure that you have a PassPhrase set on your account.

On your admin dashboard of your WHMCS site, do the following:

1. Log in to the admin dashboard of your WHMCS site and navigate to the PayFast configuration page under Setup > Payments > Payment Gateways.
2. Select Enable Recurring Billing to:
   1. Enable Subscribe Now to the tokenized billing option on invoices which requires credit card payments.
   2. Turn off Auto Redirect on Checkout under Setup > General Settings > Ordering. Set Auto Redirect on Checkout to Automatically take the user to the invoice.
   3. The Pay Now option will still be available to clients who wish to pay invoices once off.
      
3. Select Force Recurring Billing to require all clients to use tokenized billing. This requires Enable Recurring Billing to be enabled to take effect.
4. When a client has already signed up for tokenized billing:
   1. The adhoc token can be found by clicking Credit Card Information on the Client Profile page, and manually cleared by clicking Clear Details, if desired.
   2. Unpaid invoices will have the Pay Now option available so that clients can pay invoices using all once-off payment methods available on your PayFast Dashboard.
      
   3. Invoices can be automatically charged via automation settings under Setup > Automation Settings.
   4. Enables Attempt Capture functionality admin dashboard of your WHMCS site
      
5. Once the subscription has been set up, it can be managed on the Client Profile page, under the Products/Services tab on your WHMCS site admin dashboard.