Passing sdk obecjts to vCO via web services

Hello,

I am working on a PowerShell script that interacts with a vCO workflow. I have no issues passing strings, but now I need to pass an inventory object, a vCAC blueprint object to be more precisely. But I can't figure out how to include the sdk-object information into the body of the Web request.

$body = '<execution-context xmlns="http://www.vmware.com/vco">

            <parameters>

                <parameter name="description" type="string">

                    <string>Hello vCO, I am PS</string>

                </parameter>

                <parameter name="blueprint" type="vCAC:Blueprint">

                    <sdk-object> href="https://XXXXXX:8281/api/catalog/vCAC/Blueprint/59a8b719-b5b6-4676-acaa-f9c89402a3c5%252Ffad8e332-0c5b-4110-a7c8-58890e246d48/" id="59a8b719-b5b6-4676-acaa-f9c89402a3c5/fad8e332-0c5b-4110-a7c8-58890e246d48" </sdk-object>

                </parameter>

            </parameters>

         </execution-context>'

Invoke-WebRequest -uri https://XXXXXX:8281/api/workflows/516bb2af-213e-420e-9d93-b2babcdd5621/executions/ -Headers $headers -Body $body -ContentType "application/xml" -Method Post

Invoke-WebRequest : HTTP Status 409 - Parameter of type: vCAC:Blueprint did not have objectRef or id.

type Status report

message Parameter of type: vCAC:Blueprint did not have objectRef or id.

description The request could not be completed due to a conflict with the current state of the resource.

VMware vFabric tc Runtime

Any help on how to pass the object reference to the Web Request is appreciated.

Regards,

Juan.