Thanks, that was my way of thinking but I want to follow the workflow as it is now. Your proposal is to do it using some "Send" button? Or cron?

Are there any modules that are working like that so I can have a look how to do it?

I want the payment to be sent when invoice changes to "Paid" or when Account payment is set to "Paid"

What is the proper workflow?

You should build a custom module that:

1. Selects posted vendor bills that are due.
2. Creates an account.payment record in "outbound" direction.
3. Posts the payment (if conditions are met).
4. Optionally: logs, error handling, or reconciliation.
5. Later, you could:
6. 1. Hook into SEPA (via account_sepa) or use payment_acquirer subclass for custom outbound flow.
   2. Or directly post transactions to your banking API (e.g., with requests module