"Not Authorized to access " error on create mutation + GraphQL

I'm running the below GraphQL query to create data on dynamodb table, but gets the response with "Not Authorized to access createClient on type Client"

Why this is happening at.

GraphQL query:

`mutation addClient{
  createClient(input:{
    fullName: "Jhon Smith"
    title: "Software Engineer"
    organization: "AWS"
    contactNo: "+341289655524"
    email: "smithj@amazon.com"
    country: "Canada"
    address: "AN/458, Norton place, Down Town"    
  }){
    fullName
  }
}`

Response :

{
  "data": {
    "createClient": null
  },
  "errors": [
    {
      "path": [
        "createClient"
      ],
      "data": null,
      "errorType": "Unauthorized",
      "errorInfo": null,
      "locations": [
        {
          "line": 2,
          "column": 3,
          "sourceName": null
        }
      ],
      "message": "Not Authorized to access createClient on type Client"
    }
  ]
}