GB and Tyson
The biggest thing I missed in doing this was this point in the documentation:
2. Enter your SwiftCD Item Number in the "Item number" field.
It's a little bit backward in that you would think you can create everything you need in e-Junkie first and then integrate later. In fact, you have to do both together. Even though you don't explicitly pass you SwiftCD Item number to them via the Payment Variable URL
In the Payment Variable Information URL field, please enter -
They do receive it and it needs to match. I was using a more "English Friendly" Item Number and I had to change it to the SwiftCD Item Number (something like 'myproduct-001') to get everything to work together.