Please show the full/exact error message, and please use curl -i or even curl -v for more verbose logging.
Is the URL you’re using the same as given in the downlink_url attribute in the JSON payload that is posted to Hookbin? Showing us "dev_id":"myNode" in the JSON message along with /myApp/test in the URL is quite confusing, if that’s how you redacted some details.
If you’re on Windows, then see Using curl or Postman for the HTTP Integration on Windows.
Also, please show the code of your Encoder in TTN Console. (Or, if you don’t have one, then don’t use payload_fields.)