Workflow, API: text/xml

I'm trying to connect via api to add a subscriber to my ESP;

I've setup a resource, but also tried using js to webhook the variables below to convert to xml....

<ApiRequest xmlns:xsi='' xmlns:xs=''>
       <Data xsi:type='Subscriber'>













             <Value xsi:type='xs:string'>$CAMPAIGN</Value>





for the life of me, I'm not sure how to do this in a workflow