Until now an invoice you had sent could only be voided, and once it was paid not even that. That was wrong: an invoice that has left the building may not be edited or deleted, and a VAT correction belongs in a credit note tied to the original invoice number.
From a sent invoice you now credit in one action, either in full or for part of it. A separate document is created with its own number and a reference to the invoice it belongs to. The VAT is reversed and the amount stops counting as revenue anywhere.
Credit notes have their own list, their own PDF, and go out by mail the way an invoice does. For e-invoicing they carry the correct document type, including the reference to the original invoice that this requires.