Outbound REST POST always results in error

I have some code I am developing which will send a simple POST to a 3rd party system API endpoint which is shown below:

/* Create the message object */

   &msgOutbound = CreateMessage(@("Operation." | &strOperationname));

    

   /* Set the IB Info */

   &IBInfo = &msgOutbound.IBInfo;

   &bReturn = &IBInfo.LoadConnectorProp("HTTPTARGET");

   &bReturn = &IBInfo.LoadRESTHeaders();

   &IBInfo.ConnectorOverride = True;

   &IBInfo.IBConnectorInfo.ConnectorClassName = "HttpTargetConnector";

   &IBInfo.IBConnectorInfo.ConnectorName = "HTTPTARGET";

    

   &bReturn = &IBInfo.IBConnectorInfo.DeleteConnectorProperties("Content-Type");

   &bReturn = &IBInfo.IBConnectorInfo.AddConnectorProperties("Content-Type", &strContentType, %HttpHeader);

   If All(&strAuthorization) Then

     &bReturn = &IBInfo.IBConnectorInfo.DeleteConnectorProperties("Authorization");

     &bReturn = &IBInfo.IBConnectorInfo.AddConnectorProperties("Authorization", &strAuthorization, %HttpHeader);

   End-If;

   &bReturn = &IBInfo.IBConnectorInfo.DeleteConnectorProperties("URL");

   &bReturn = &IBInfo.IBConnectorInfo.AddConnectorProperties("URL", &strURL, %HttpProperty);

   &bReturn = &IBInfo.IBConnectorInfo.DeleteConnectorProperties("Method");