I'm using the Ruby SDK to make a POST request to create a subscription in the sandbox environment. The WebHook address is a local tunnel to my local app server, and I see the request coming through and responding with 200 OK.
Here's the error I'm getting from the request to the subscription API:
SUB-521 WebHook is not reachable
It is reachable, and the request is completing, after successfully sending the Verification-Token header. (Otherwise I would be getting SUB-520 I believe.)
Any clues what's going wrong? Is there some sort of payload it is expecting to receive beyond the Verification-Token?
app key => nDaskd-URlGBOsj0N4Ilnw