How to use SEPA direct debit for customers?

I want customers pay via direct debit. I understood, that I need to

  • add an bank account to the party
  • add SEPA direct debit mandate
  • check “direct Debit” in Party→Accounting
  • … some parts missing here …
  • export direct debit file for online-banking software

What I did not yet understand:

  • How to mark an invoice as “to be payed by direct debit” (in my mental model this would be a payment term)
  • How to create the respective direct debit information to be exported
  • How to actually export the direct debit information