How to upload a list of contacts using Qualtrics create contact API?

Hello All,
I am trying to trigger a JSON event with the JSON payload as below -
{
 "contacts": [{
  "lastName": "L1",
  "extRef": "'20'",
  "email": "a@test.com",
  "firstName": "A1",
  "phone":"'9876543210'"
 },
 {
  "lastName": "L2",
  "extRef": "'21'",
  "email": "a2@test.com",
  "firstName": "A2",
  "phone":"'9876543200'"
 }]
}
Post this I am calling the Qualtrics Contact API webservice task to create contact but it fails as instead of sending one set of contact data, I am currently sending list of contact data.
Is there any way to upload a list of contacts and create contacts in Qualtrics? Has anyone tried to upload similarly?
Any help on how I can achieve this? Thanks!