In your form editor’s E-commerce section add the payment gateway you want to use and tick the Use recurrent payment option. Next, set a regular basis when the client is billed (per days, weeks, months and years). That’s all that differentiates a subscription from a one-time payment. Payment gateways that support recurrent payment will have this option displayed in the integration box. Make sure you’ve assigned the prices on your order form.
For PayPal and PayPal Pro you can also add the number of recurring payment cycles. This means you will limit the number of times the recurrent payment is applied.
Not all payment gateways have recurring payments. Here is our Payment Gateways Comparison Chart for more details.
If you are using another version, check out this article with the same subject.