Bumping this. For each of these I tried both headers of apikey->(actual API key) and partnerapikey->(actual api key)
Here is what I've tried and why:
1) Returning a JSON message with the response key: {"responseKey":(actual response key)}
2) Returning a plain text message with just the response key. Tried this because the documentation says "The partner must return this and only this in the response content"
3) Returning the whole message back. I tried this because the documentation says "Before downloading the content, Roku checks to ensure that the size is equal to the size of what was sent".
Unfortunately, none of these worked. Can we please get this explained and/or added to the documentation?