Can a Customer opt out of automated invoice payments and still use the direct debit payment method?

Yes, when the Customer has direct debit as the default payment method, but also opted out of or cancelled automated invoice payments, direct debit can still be used as a payment method. To make payment for invoices, you will have to manually initiate the payment from your dashboard.

See also: Pay invoice via debit/credit card or manually via ACH/SEPA direct debit