Additional page with payment slip for invoices?

I need to add an additional page (with a payment slip) to the existing invoice template.

The payment slip itself is not the problem, I already have a working (standalone) pdf creation code solution.
But where exactly do I have to “inject” this additional pdf page to the ready-to-create-pdf-invoice?

Which php routine or code line should I inspect to find the place for my additional page?

Hi,
The payment details are indicated in the Invoice itself.

That how exactly helps me to find the code line where I can “inject” the additional pdf page? :wink:

What I was suggesting is that you don’t need a additional page with payment since the first page of the invoice will have the payment details.