Automation to send web request /incoming webhook authentication between 2 jira platforms

[Ben Alderton]

I have 2 jira instances. I want to use a "send web request" automation rule using POST from one instance to the other, using an "incoming webhook" to receive it, to effectively clone certain tickets matching some conditional logic.

I have tried to authenticate the "Send web request" using Base64 encoded API key, and also use the secret generated from instance B "incoming webhook" component, but always receive error 400 bad request with the following payload.

Where am I going wrong?

{
  "errorMessage": null,
  "message": null,
  "warningMessages": [],
  "errorMessages": [
    "Missing token"
  ],
  "errors": {},
  "status": 400
}