Anyone experience with the SAP Punch-out catalog structure (OCI)?

I am building an integration with the customer's SAP system whereby they can access our webshop and transfer the order to their system for internal processing. The problem that I face is the lack of documentation and support about this integration. Especially the part around the order transfer is not clear.
We know that the OCI standard is used meaning that the communication is done via the POST method (thus http not xml). We also know the structure and the mandatory fields. However the post implementation itself still doesn't work.

My question: does have anyone experience with intergration OS to SAP via OCI?