The full list of SAP SRM PunchOut Call-Up Parameters explained:
This post will explain the different return or Call-up Parameters from an External Punch Out
Parameters
SAP Screen Personas 3.0 URL Parameters available
Personas 3.0 URL Parameters: This document will provide a list of URL parameters that can be used in SAP Screen Personas 3.0 launch URL.
Also check out the related KB articles listed at the bottom of this article.?