How can I retrieve the ID of a custom section for a test plan?

I am trying to build a template in RPE to pull text from custom rich text sections of a test plan. Almost everything I've found on this topic points back to this thread: https://jazz.net/forum/questions/89659/print-custom-section-in-rqm-using-rpe

In working through the first steps for the solution, (in Collin's 'completed' comment) Collin points out that you must find the ID of the custom sections and provides a URI which should return that information in step 3. When I preview this URI in rpe launcher on a test plan that was created from a test plan template with the desired sections and has no text inserted, I get xml returned. When I access this URI on the same test plan but with text added in the custom sections, the data preview only returns the text that was added to those sections, but no xml on the test plan artifact, any artifacts associated with the test plan or the custom sections themselves that I'm interested in. Because there's no xml, I have no section IDs to reference for the solution. Am I missing something?