Any solutions to this? I am getting webhooks from my assistant through having a Server URL on my Phone Number in VAPI. I am returning a response to the webhook type

assistant.started

However my Vapi assistant doesn't do anything with this response - as in - I'm returning the following and it doesn't change it's output:

{
  "assistant": {
    "firstMessage": "Hi Joe, welcome back! How can I help you today?",
    "model": {
      "messages": [
        {
          "role": "assistant",
          "content": "This is an existing customer named Joe"
        }
      ]
    }
  }
}