I actually have managed to get a payment to complete confirming that the API is working but it is not being accomplished automatically by running the cron. This is the only way I can get it to work:

After a user check out and selects steem as payment:

They are then redirected to the Steem Payment Page:

They must then proceed to make the payment and return to their account where they see the following:

When they click PAY as shown in the previous image they see the following:
(Note the missing fields, there is no need to click PROCEED TO STEEM here)

ONLY after they have completed the previous steps and the Cron has run do we have success:

I went through this entire process step by step including checking out and re-visiting the My Acccount page and clicking PAY before any payment was made and then running the Cron so I can confirm that the payment must actually be made before it actually marks as completed.

Dev, Please advise. This is driving me crazy!