GraphQL: Returning errors on a schema

Help Hub
1

Dear All,
I am writing unto you regarding the GraphQL Schema. I have some errors whilst I am generating a GraphQL API. Therefore , I can’t fetch the schema.
Where may I find information regarding the GraphQL schema on Postman? What is considered a valid GraphQL schema in Postman ?

I hope to hear from you.

[Not a valid graphQL Schema ?]

1.Apollo_GraphQL
1.Apollo_GraphQL1912×874 200 KB

[Can’t fetch the schema]

2.ApolloGraphQL_fetching_Schema
2.ApolloGraphQL_fetching_Schema1909×928 217 KB

listings.graphql

extend schema
   @link(url: "https://specs.apollo.dev/federation/v2.11", import: ["@key"])
    @link(url: "https://specs.apollo.dev/connect/v0.1", import: ["@source","@connect"])
    @source(
      name: "listings"
      http: { baseURL : "https://airlock-listings.demo-api.apollo.dev"}
    )

type Query {
   "A curated array of listings to feature on the homepage"
   featuredListings: [Listing!]! @connect(
     source: "listings"
     http: { GET: "/featured-listings" }
     selection: """
       id 
       title
       numofBeds
       CostPerNight
     """
   )
   "A specific listing"
   listing(id: ID!): Listing
   @connect(
     source: "listings"
     http: { GET: "/listings/{$args.id}" }
     selection: """
      id
      title
      numofBeds
      CostPerNight 
     """
   )
}

"A particular intergalactic location available for booking"
type Listing {
   id: ID!
   "The listing's title"
   title: String!
   "The number of beds available"
   numofBeds : Int
   "The cost per night"
   CostPerNight : Float
}

Thank you very much.