accConPostRequest.json

{
  "compositeRequest": [
    {
      "method": "POST",
      "url": "/services/data/v52.0/sobjects/Account",
      "referenceId": "newAccount",
      "body": {
        "Name": "Acme Inc."
      }
    },
    {
      "method": "POST",
      "url": "/services/data/v52.0/sobjects/Contact",
      "referenceId": "newContact",
      "body": {
        "LastName": "Smith",
        "FirstName": "John",
        "AccountId": "@{newAccount.id}"
      }
    }
  ]
}