Problem creating fulfillmentService

[lenaAlvarez]

Hi, I neet to build an app for fulfillment services, I am trying to create a fulfillment service with this mutation

mutation fulfillmentServiceCreate($name: String!, $callbackUrl: URL!) {

    fulfillmentServiceCreate(name: $name, callbackUrl: $callbackUrl) {

      fulfillmentService {

        id

        serviceName

        callbackUrl    

        location {

          id

        }

      }

      userErrors {

        field

        message

      }

    }

  }
and I have an issue because the response came empty
{FulfillmentService:{Id: Location:{Id:}} UserErrors:[]}
I made sure that mi callbackUrl is right and returns 200, the accessToken is right and the name of my shop
but I am still getting an emptyResponse, When I go to admin panel of shopify I can see my fulfilmentServices created before

I need ypur help please.