Well this morning was a huge success, I had a 5 minute chat with Kevin from CampMinder about the CampMinder StaffHire, So Close issues we were experiencing. It turns out that we format our salary information in a way which is incompatible with their server, adding a , was resulting in the inconsistent POST errors we were seeing yesterday.
We updated the codebase, and have since updated the library specs to reflect this requirement and are now consistently recieving success messages for our POST.
With that solved I was able to finish up the remaining small stories and send everything out for acceptance. We should be able to go live with CampMinder next week, closing this chapter of interesting work.