How to Perform an HTTP Post using a REST API and Using the Msxml2 DLL

Hello all. Trying to perform an HTTP POST operation using the Msxml2 DLL and a JSON payload. From all documentation, research with other developers, etc. it appears that I have most everything correct, yet I am getting ISE's (500). Web service provider hasn't been any help with diagnosing, so I have been left to try to figure it out on my own.

What DOES work:

- All GET operations, using a small variant in URL, and returning the expected JSON response.
- All operations (GET and POST) call for an authorization header, and an accept header, shown below, and working for the GET operations:
hdHTTP:setRequestHeader("Authorization", p-token).
hdHTTP:setRequestHeader("Accept","application/json; charset=UTF-8").

The only difference (according to the documentation) with the POST operation that fails is that it:

- is a POST - verified
- has a slightly different URL (for the resource) - verified
- requires a JSON payload - verified with another developer's working JSON payload

Obviously, the payload has to be specified somewhere, and I thought that it should be in the .Send method, as in:

Is this the correct place to insert the payload?