How do I add my bank account / payment instructions to invoices?

The cleanest way is to set up a financial account under Business settings → Financial accounts. Add the account name, IBAN, SWIFT/BIC, and bank name — these appear in a dedicated section on every invoice you issue, in the right place for your customer's accountant to find them. See Financial accounts for the full setup.

If you need extra payment instructions on top of the bank account — for example "Please use the invoice number as the payment reference" — add them to the default notes field. The bank account stays in its dedicated section, and your custom note appears alongside it. See How do I add notes that always show on my invoices?.