Dear Jeffrey,
I am PHP expert with 6 yrs of experience, and have an extensive experience in dealing with APIs.
I checked out the API documentation, and I can deal with the API, as fortunately, all the APIs are almost the same in talking to, and in their structure (edit, post, read, write).
All I need is a list of features that you will need to perform exactly, and I will build the script based on that.
I understood that you need a backend script for updating/sync information across the 2 systems you have. :)
Please message me to discuss it in detail and get started.
Waiting for your answer and thanks in advance.