As I understand it, I have no way of controlling the endpoint details so it wouldn't matter what I did, or may have done, at any stage in this process.
I, personally, suspect yet another bug with eCart and either I've just been extremely unlucky here or there are actually some issues with the extension - either way, I don't feel responsible for any of it and I would appreciate, after two weeks struggling to get this working, a prompt resolution. Thank you.
NJ