When trying to enable a webhook, I am getting this error:
Unable to parse request. The following error occurred: Unknown attribute "smartsheetHookResponse"
From the documentation
The subscriber responds to the verification request by echoing back the same unique random value in the Smartsheet-Hook-Response header of the response. For API clients that don't interpret header values, you can also send a JSON body with a smartsheetHookResponse attribute and the same value that would have been in the header.
When I receive the callback my app responds with a PUT request and { "smartsheetHookResponse": <challenge.value> } as JSON body.