ProSites Field Missing From WHMCS

Hi, I have recently integrated my multisite with your awesome ProSites plugin and combined it with the handy WHMCS Provisioning plugin. Everything is from a fresh installation and seemed to be working well...

When I came to test the signup process again later, I realised that WHMCS was clueless to the different ProSite levels that I had added since integrating it. I looked back over the documentation to see what needed to be done and saw that I needed to add a ProSite name to the module settings of each product.

The issue I'm having is that the field does not exist.

What I should see:

What I am seeing:

It's probably (and hopefully) something painfully obvious but any help would be greatly appreciated!