Sidebar, comments are illegal in JSON so what you are handling is not JSON and neither is the "Json text" in your original __DATA__. decode_json was surely telling you so with malformed JSON string, neither tag, array, object, number, string or atom, at character offset 0 (before "Json text") or garbage after JSON object.

If it were me, I'd report it to the owner of the application issuing it. Issuing, and accepting if you can help it, broken data is a worst practice.