Autopay requirement for existing students.

My business is in the UK. We have found that it is easier handling new students' registration via admin with a sign-up form as per having parents register via portal and add information, as they usually don't finish setting up the account as they couldn't be bothered or leave information blank, thus, we lose out on a new student or have additional work by trying to ensure they complete their accounts.

The only problem is when we add and register students from admin it gives them autopay as an option and does not require it when making their first payment after we post tuition, I have tried to find a way to ensure they sign up to autopay, but we have had a few parents do runners and am now needing to have an option to ensure we have all students enrol in autopay when making their first payment and to not offer this as an option. How do we do so without making this an "option". Even when I tick settings "require autopay" it only allows it for new registrations and does not offer this option to already existing customers.

Please help!