Thanks for writing, Corey. And good find.
I must admit, I don't recall the full history of the implementation with respect to destinations. But something broke down along the way. The API code is looking for the cryptic Metro endpoint references, which are numbers and not names. For example, "ETP" is represented by the number 109. The API documentation clearly references the names.
I'm investigating a solution that will do a translation from "ETP" to the underlying resource number. I'll let you know what I find.
Cheers.
Greg