I'd suggest that the system should allow for additional information to be added to the invoice based upon the payment method.
At the moment if the payment will be taken via DirectDebit through GoCardless, all that's added is a "PAID" stamp.
I think the customer should be given a little more information.. I include info in the PDF template to let the customer know what's really happening, mentioning that the payment will come out via direct debit over the next few days.
However if I were to send an invoice that required manual payment (not taking a direct debit payment via GoCardless) then this note about Direct Debit would not be appropriate.
Having payment options and bank details noted would be more suitable.
The PDF template can currently be changed per customer, but not per payment method.
Suggested solution -
If each payment method had it's own field: 'Invoice notes'.. that would make things much simpler, explaining how the customer should respond to the invoice.