Appsync Subscriptions not working , but queries and mutations are working fine - android-emulator

Question

I am building a simple React Native app. to test AppSync APIs. I am able to do queries, mutations ; but subscriptions don't seem to work. I am trying this out on an Android Emulator.
Here's how i am building my client and creating a subscription.
const client = new AWSAppSyncClient({
url: awsconfig.aws_appsync_graphqlEndpoint,
region: awsconfig.aws_appsync_region,
auth: {
type: AUTH_TYPE.API_KEY, // or type: awsconfig.aws_appsync_authenticationType,
apiKey: awsconfig.aws_appsync_apiKey,
}
});
subscription = client.subscribe({ query: gql(onCreateBook) }).subscribe({
next: data => {
console.log("got a book--->");
},
error: error => {
console.warn("errror getting book");
}
});
Here is my schema(relevant parts) & subscriptions gql(auto generated by codeGen)
Schema
type Book {
title: String!
description: String
}
type Mutation {
createBook(input: CreateBookInput!): Book
updateBook(input: UpdateBookInput!): Book
deleteBook(input: DeleteBookInput!): Book
}
type Query {
getBook(title: String!): Book
listBooks(filter: TableBookFilterInput, limit: Int, nextToken: String): BookConnection
}
type Subscription {
onCreateBook(title: String, description: String): Book
#aws_subscribe(mutations: ["createBook"])
onUpdateBook(title: String, description: String): Book
#aws_subscribe(mutations: ["updateBook"])
onDeleteBook(title: String, description: String): Book
#aws_subscribe(mutations: ["deleteBook"])
}
subscriptions gql
// eslint-disable
// this is an auto generated file. This will be overwritten
export const onCreateBook = `subscription OnCreateBook($title: String, $description: String) {
onCreateBook(title: $title, description: $description) {
title
description
}
}
`;
export const onUpdateBook = `subscription OnUpdateBook($title: String, $description: String) {
onUpdateBook(title: $title, description: $description) {
title
description
}
}
`;
export const onDeleteBook = `subscription OnDeleteBook($title: String, $description: String) {
onDeleteBook(title: $title, description: $description) {
title
description
}
}
`;
Note : I have verified that subscriptions are working fine on firing a mutation in AWS Console, but i cant see any errors in ReactNative app.