Getting field mask when try to access ads data

[Arunim Malviya]

I am getting fieldmask for some some parameters, i generated the query using GAQL (https://developers.google.com/google-ads/api/fields/v17/ad_query_builder)
endpoint: POST https://googleads.googleapis.com/v17/customers/3940771942/googleAds:search
Authorization: OAuth token is passed
Headers: {developer-token:MqOEfgEnvf-b_0_aH4P4gg; login-customer-id:3452384805}
AccessToken: Valid access token
Body: {
  "query": "SELECT ad.app_ad.descriptions, ad.app_ad.headlines, ad.app_ad.images, ad.display_url, ad.name FROM ad"
}
Response:
{
    "results": [
        {
            "ad": {
                "resourceName": "customers/3940771942/ads/701711376954"
            }
        },
        {
            "ad": {
                "resourceName": "customers/3940771942/ads/701711535765"
            }
        },
        {
            "ad": {
                "resourceName": "customers/3940771942/ads/701735644270"
            }
        },
        {
            "ad": {
                "resourceName": "customers/3940771942/ads/705319515342"
            }
        },
        {
            "ad": {
                "resourceName": "customers/3940771942/ads/705422710988"
            }
        },
        {
            "ad": {
                "resourceName": "customers/3940771942/ads/705422738042"
            }
        },
        {
            "ad": {
                "resourceName": "customers/3940771942/ads/705423183287"
            }
        },
        {
            "ad": {
                "resourceName": "customers/3940771942/ads/706253803112"
            }
        }
    ],
    "fieldMask": "ad.appAd.descriptions,ad.appAd.headlines,ad.appAd.images,ad.displayUrl,ad.name",
    "queryResourceConsumption": "312"
}
I have all necessary scopes and permissions