Getting Graphql error while doing serverless deploy

I am using serverless appsync plugin and deploying it to my aws account by following Part 03: AWS AppSync: Resolver Mapping Templates | Serverless Framework & AWS Amplify - YouTube.
I managed to get the initial resources deployed uisng cfn. however when deploying the graphql resources to create API, it is failing to save graphql schema.

error stack:

8c859063389c:backend jaydevn$ sls deploy
AppSync Plugin: GraphQl schema valid
Serverless: Packaging service...
Serverless: Uploading CloudFormation file to S3...
Serverless: Uploading artifacts...
Serverless: Validating template...
Serverless: Updating Stack...
Serverless: Checking Stack update progress...
Serverless: Operation failed!
Serverless: View the full error output:
 Serverless Error ----------------------------------------
  An error occurred: GraphQlSchema - Schema Creation Status is FAILED with details: Internal Failure while saving the schema..


service: serverless-appsync-backend
frameworkVersion: '2'

  name: aws
  runtime: nodejs12.x
  lambdaHashingVersion: 20201221
  stage: dev
  region: us-east-1


  - serverless-appsync-plugin

    name:  serverless-appsync-backend
    # apiKey # only required for update-appsync/delete-appsync
    # apiId # if provided, will update the specified API.
    authenticationType: AMAZON_COGNITO_USER_POOLS
      awsRegion: us-east-1
      defaultAction: ALLOW
      userPoolId: !Ref cognitoUserPool
    mappingTemplatesLocation: mapping_templates
      - dataSource: booksTable
        type: Query
        field: getBookById
      - dataSource: booksTable
        type: Mutation
        field: createBook 
      - type: AMAZON_DYNAMODB
        name: "booksTable"
        description: "books ddb table"
          tableName: !Ref booksTable


schema {
  query: Query 
  mutation: Mutation

type Query {
  getBookById(bookId: ID!): Book!
  listBooks(limit: Int!, nextToken: String):BooksPage!
  myOrders(limit: Int!, nextToken: String): OrderItemsPage!

type OrderItemsPage {
  orderItems: [OrderItem]
  nextToken: String
type OrderItem{
  userId: ID!
  orderId: ID!
  book: Book!
  quantity: Int!

type BooksPage{
  books: [Book]
  nextToken: String

type Book{
  bookId: ID!
  title: String!
  description: String!
  imageUrl: AWSURL
  author: String!
  price: Float!
  createdAt: AWSDateTime!
  updatedAt: AWSDateTime!

type Mutation{
  createBook(newBook: BookInput): Book! @aws_auth(cognito_groups: ["admin"])
  createOrder(newOrder: OrderInput): Boolean!
type OrderInput{
  items: [OrderItemsInput]
type OrderItemsInput{
  bookId: ID!
  quantity: Int!
type BookInput{
  title: String!
  description: String!
  imageUrl: AWSURL
  author: String!
  price: Float!

I am unable to understand how should I resolve this. Thanks in advance!

tried redeploying in another region, updated node version, deleted teh stack completely and deploying a fresh one. still no help.

Where can I find the exact internal error/failure that is causing cloudformation step to fail?

I don’t know if you have already solved this, but today I had the same issue when mistakenly using inputs an types interchangeably. In your case I can notice OrderInput and BookInput are types and not inputs.
Also remember not to have an input be the field of a type or viceversa. That was my mistake and it was not noticed by the compiler (although I use amplify instead of serverless for this).