You can enable or disable autopay in the Payment Methods section of the Account dropdown on your Leif dashboard.
If autopay is disabled, your ISA payments will still be scheduled pursuant to the terms of your ISA contract. You will need to manually complete your payments via your Leif dashboard (on the Payments page). As stated in the ISA, you are responsible for making timely payments. You will receive reminders and escalated communications if you have any overdue payments.