I finally decided to use the magento cart plugin, but I get a message that the api key is invalid. I know the SSL is all set up correctly.
One problem I have is that the SSL SHA1 fingerprint field is only long enough if I strip the : characters out of the signature, so I have to either remove the :s or use a truncated version of the fingerprint. Could this maybe be a bug from the new site design?
I had the same problem! The field is not long enaugh to inset the complete fingerprint