Oh, ok, that makes sense. I am having the same exact problem with this site: adamhsukungfu.com. Here's the page:
http://www.adamhsukungfu.com/adam-hsu-dvds/
I upgraded from the last version of shopsite plugin to the current one and it went from working to not working (it looks like it is not backward comatible? Can it be that all the codes need to be changed now?) for the first DVD on the page I have pasted the new codes...the rest of them are the old codes, but none show up, and I removed the s from https in the callback url.
Ugh, and thanks!