How to resolve "must provide at least 1 valid contact" in response of Qualtrics API?

I'm currently working in Contacts import of Qualtrics API and I'm getting a response of "must provide at least 1 valid contact" here is my body in API. Here is my fields in Qualtrics and API. Thank you in advance


{
  "transactionMeta" : {
      "batchId": "----",
      "fields": [
        "FirstName",
        "LastName",
        "email",
        "phone",
        "language",
        "extRef"
      ]
  },
  "contacts": [
    {
        "FirstName": "Test",
        "LastName": "Data",
        "email": "example@sample.com",
        "phone": null,
        "language": null,
        "extRef": "244466666"
    }
  ]
}