Are you getting this response when trying to send data to your incoming webhook?
This is the default error response from the incoming webhooks system, and if you're receiving this it's most likely due to one of two things.
1) You're not sending the authentication header correctly
Note that aside from a custom URL, in the web-hook setup you also receive a specially generated "Emercury Key". Please note that this key is different than your general account-level Emercury API key. This is a key specific to this particular incoming web-hook only.
You need to send this key in the http headers with every request. Include this key in a header called emercury-api-key.
Note that the http header is named differently than in the setup interface. So be sure to copy it if you want to make sure you're sending the exact header, or otherwise you will receive the same error message.
2) You haven't set up the web-hook by listening first
You need to click on the "Start Listening" button, and then send an initial first testing request; then map the received data from this initial test request, and save the web-hook. Only after this is done future requests will work to update a subscriber. For successful requests you will see the following response instead of "waiting".