Firebase Cloud Messaging - Posting Message Says In

Question

So I'm using jQuery Ajax to post using a bearer token that I'm having to get from someone's node.js app because I can't find Google docs on how to use your preferred language to get a bearer token for FCM use only. I'm using JSON.stringify to prepare the payload data which someone shows on stackoverflow here. I've tried without but I just get a basic error message of Invalid_Arguments. Using JSON.stringify shows more to the error. It's stating that "to" and "notification" properties are unknown names but those are the property names used in Google docs. So what am I doing wrong?

Here's the link where someone says JSON.stringify works. Before then I tried without JSON.stringify which led to Invalid JSON Payload and my reason for asking this question.

send post request to firebase cloud messaging by ajax?

{
  "error": {
    "code": 400,
    "message": "Invalid JSON payload received. Unknown name \"to\": Cannot find field.\nInvalid JSON payload received. Unknown name \"notification\": Cannot find field.",
    "status": "INVALID_ARGUMENT",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.BadRequest",
        "fieldViolations": [
          {
            "description": "Invalid JSON payload received. Unknown name \"to\": Cannot find field."
          },
          {
            "description": "Invalid JSON payload received. Unknown name \"notification\": Cannot find field."
          }
        ]
      }
    ]
  }
}


$.post({
            method: "POST",
            url: "https://fcm.googleapis.com/v1/projects/floridarecycling-b91ec/messages:send",
            dataType: "json",
            contentType: "application/json",
            headers: {
                'Authorization': 'Bearer ' +
                    'ya29.c.ElqUBiCx...wyKqUqKlrg7yhPw'
            },
            data: JSON.stringify({
                "to": "user_token",
                "notification": {
                    "title": "Test",
                    "body": "test"
                }
            })
            success: function () {
                console.log("Success")
            },
            error: function (err) {
                console.log("error ", err)
            }
        });`