Hello, I have a custom module that takes a sales order, and processes a credit card payment.  What I want to do is create an invoice when the credit card payment is approved and mark the invoice as paid following as closely to the invoicing workflow as possible.  So far my module does this:

1.  Processes the credit card

2.  Makes an invoice if payment is approved

3.  Validates the invoice and puts it in the Open state.

The next step would be to register the invoice as paid but Im not sure how the workflow actually does it.  Does anyone know which steps occur when the invoice is getting paid?