Documentation for the XML, REST, and SOAP APIs resides here:
https://www.propay.com/en-US/Resources#APIDocs
For reporting, go to this page:
You may not find some older or less-frequently used solution manuals on these pages, so if you don't see what you're looking for, you can send and email to Client Support requesting it.
Partners may find additional helpful resources to integrate ProPay's solutions into theirs at developer.propay.com.