How do I add backend rule to the API service config file? - openapi

Question

Trying to create an API for the first time in GCP and getting the following error
ERROR: (gcloud.api-gateway.api-configs.create) API Config's backend has no rules. If using gRPC, be sure to specify the 'rules[]' under the 'Backend' field. See https://cloud.google.com/endpoints/docs/grpc-service-config/reference/rpc/google.api#backendrule for more details.
However, if I try to add a backend to the yaml file, I am getting the following error.
ERROR: (gcloud.api-gateway.api-configs.create) INVALID_ARGUMENT: Cannot convert to service config.
'location: "unknown location"
kind: ERROR
message: "Invalid OpenAPI file. Please fix the schema errors:\nerror: object instance has properties which are not allowed by the schema: ["backend"]\n level: "error"\n schema: {"loadingURI":"http://swagger.io/v2/schema.json#","pointer":""}\n instance: {"pointer":""}\n domain: "validation"\n keyword: "additionalProperties"\n unwanted: ["backend"]"
This is the bare bones yaml file I am using.
swagger: '2.0'
info:
title: sayHello
version: '1.0'
description: sayHello
schemes:
- https
produces:
- application/json
consumes:
- application/json
backend:
rules:
- selector: "*"
address: https://abc.cloudfunctions.net/sayHello
paths:
'/getPoints/{clientId}':
parameters:
- type: string
name: clientId
in: path
required: true
definitions: {}
responses:
'200':
description: Success
schema:
type: string
examples: {}
headers: {}
What am I missing? Somehow, not able to find much resources around adding backend rules to the service config file. Not even able to get the spec to validate against.
Any help would be appreciated.