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?
request uri => https://platform.devtest.ringcentral.com/restapi/v1.0/subscription
app key => nDaskd-URlGBOsj0N4Ilnw