It’s quite simple. You can access the subscription payment feature from the button of the form setting, when creating a  form. Follow these simple steps to create a recurring payments form:
Navigate to Forms in the FormPay app.
Name your form and choose the HubSpot form. In addition to this, select the redirection/thank you page settings, payment settings & payment method (gateway).
After this, enable the Allow Subcription toggle under Subscription Settings.
Then, select Recurring in the payment type.
Choose Monthy
Note: Only Stripe & Authorize.net can enable subscription. Also, Subscription settings can only be enabled when you disable Donation Settings in the Form tab.