Resource handler returned message: "No integration defined for method (Service: ApiGateway, Status Code: 400

Question

I want to import a YAML file into API GateWay. Whenever I do so I get the following error

Resource handler returned message: "No integration defined for method (Service: ApiGateway, Status Code: 400

I use the following code to import the YAML file

const integration = new LambdaIntegration(hello)

const api = new SpecRestApi(this, 'books-api', {
  apiDefinition: ApiDefinition.fromAsset('apiTrial.yaml')
});

const booksResource = api.root.addResource('books')
booksResource.addMethod('GET', integration);

});

and my current yaml file is:

openapi: 3.0.0
info:
  title: "MyFirstAPI"
  version: "1.0.0"
  contact:
    name: Karim Fayed
    email: [email protected]
    url: https://example.com/
tags:
  - name: Metadata
    description: Metadata related requests
servers:
- url: "https://api.openweathermap.org/data/2.5"
paths:
  /:
    get:
      operationId: getMetadata
      summary: Get metadata from the root of the API
      tags: [ 'Metadata for root' ]
      responses:
        '200':
          description: OK
  /weather:
    get:
      operationId: "getMetadata"
      summary: "Get metadata from weather API"
      tags: ["metadata data for wather"]
      responses:
       200:
        description: successful operation
       400:
        description: Invalid id supplied
       404:
        description: Contact not found
       500:
        description: Server error

As you can see I already have a response for code 400 so why would the error keep showing up?