How do I set up Medline punchout with a punchin url?

We are looking to set up a punchout for Medline SuisteStyles. Our rep is saying that in addition to the punchout URL there needs to be a way to send back the PO to them via a punchin URL. We have other punchouts in our system but they are set up EDI. This Medline SuiteStyles can not be set up EDI according to the rep. How and where do I add the punchin url in the catalog set up? Is there any other customer using Medline SuiteStyles as a punchout that can provide some guidance on the set up? Thanks!