Microsoft graph webook validation token issue

I created an endpoint for the MIcrosoft Graph Webhook API but for some reason, the validation token returned isn't correct. It shows

Validation: Testing client application reachability for subscription Request-Id:

Any help would be appreciated

{
  "resource": "/enpoing",
  "httpMethod": "POST",
  "queryStringParameters": {
    "validationToken": "Validation: Testing client application reachability for subscription Request-Id: 481f1e66-d235-4e98-9205-bfb917760877"
  },
  "multiValueQueryStringParameters": {
    "validationToken": [
      "Validation: Testing client application reachability for subscription Request-Id: 481f1e66-d235-4e98-9205-bfb917760877"
    ]
  }
}

from Microsoft graph webook validation token issue