AWS CDK and AppSync: Invalid principal in policy: "SERVICE":"appsync" - amazon-web-services

Question

I'm trying to follow tutorials and use AWS's CDK CLI to deploy a stack using AppSync and some resource creations fail with errors like the following showing under events for the Stack in the CloudFormation console:
Invalid principal in policy: "SERVICE":"appsync" (Service: AmazonIdentityManagement; Status Code: 400; Error Code: MalformedPolicyDocument; Request ID: 8d98f07c-d717-4dfe-af96-14f2d72d993f; Proxy: null)
I suspect what happened is that when cleaning up things on my personal developer account I deleted something I shouldn't have, but due to limited AWS experience I don't know what to create, I suspect it's an IAM policy, but I don't know the exact settings to use.
I'm trying on a new clean project created using cdk init sample-app --language=typescript. Running cdk deploy immediately after the above command works fine.
I originally tried using cdk-appsync-transformer to create GraphQL endpoints to a DynamoDB table and encountered the error.
I tried re-running cdk bootstrap after deleting the CDKToolkit CloudFormation stack, but it's not fixing this problem.
To rule out that it's due to something with the 3rd party library, I tried using AWS's own AppSync Construct Library instead and even following the example there I encountered the same error (although on creation of different resource types).
Reproduction steps
Create a new folder.
In the new folder run cdk init sample-app --language=typescript.
Install the AWS AppSync Construct Library: npm i #aws-cdk/aws-appsync-alpha#2.58.1-alpha.0 --save.
As per AWS's docs:
Create lib/schema.graphql with the following:
type demo {
id: String!
version: String!
}
type Query {
getDemos: [ demo! ]
}
input DemoInput {
version: String!
}
type Mutation {
addDemo(input: DemoInput!): demo
}
Update the lib/<projectName>-stack.ts file to be essentially like the following:
import * as appsync from '#aws-cdk/aws-appsync-alpha';
import { Duration, Stack, StackProps } from 'aws-cdk-lib';
import * as dynamodb from 'aws-cdk-lib/aws-dynamodb';
import * as sns from 'aws-cdk-lib/aws-sns';
import * as subs from 'aws-cdk-lib/aws-sns-subscriptions';
import * as sqs from 'aws-cdk-lib/aws-sqs';
import { Construct } from 'constructs';
import * as path from 'path';
export class CdkTest3Stack extends Stack {
constructor(scope: Construct, id: string, props?: StackProps) {
super(scope, id, props);
const queue = new sqs.Queue(this, 'CdkTest3Queue', {
visibilityTimeout: Duration.seconds(300)
});
const topic = new sns.Topic(this, 'CdkTest3Topic');
topic.addSubscription(new subs.SqsSubscription(queue));
const api = new appsync.GraphqlApi(this, 'Api', {
name: 'demo',
schema: appsync.SchemaFile.fromAsset(path.join(__dirname, 'schema.graphql')),
authorizationConfig: {
defaultAuthorization: {
authorizationType: appsync.AuthorizationType.IAM,
},
},
xrayEnabled: true,
});
const demoTable = new dynamodb.Table(this, 'DemoTable', {
partitionKey: {
name: 'id',
type: dynamodb.AttributeType.STRING,
},
});
const demoDS = api.addDynamoDbDataSource('demoDataSource', demoTable);
// Resolver for the Query "getDemos" that scans the DynamoDb table and returns the entire list.
// Resolver Mapping Template Reference:
// https://docs.aws.amazon.com/appsync/latest/devguide/resolver-mapping-template-reference-dynamodb. html
demoDS.createResolver('QueryGetDemosResolver', {
typeName: 'Query',
fieldName: 'getDemos',
requestMappingTemplate: appsync.MappingTemplate.dynamoDbScanTable(),
responseMappingTemplate: appsync.MappingTemplate.dynamoDbResultList(),
});
// Resolver for the Mutation "addDemo" that puts the item into the DynamoDb table.
demoDS.createResolver('MutationAddDemoResolver', {
typeName: 'Mutation',
fieldName: 'addDemo',
requestMappingTemplate: appsync.MappingTemplate.dynamoDbPutItem(
appsync.PrimaryKey.partition('id').auto(),
appsync.Values.projecting('input'),
),
responseMappingTemplate: appsync.MappingTemplate.dynamoDbResultItem(),
});
//To enable DynamoDB read consistency with the `MappingTemplate`:
demoDS.createResolver('QueryGetDemosConsistentResolver', {
typeName: 'Query',
fieldName: 'getDemosConsistent',
requestMappingTemplate: appsync.MappingTemplate.dynamoDbScanTable(true),
responseMappingTemplate: appsync.MappingTemplate.dynamoDbResultList(),
});
}
}
Run cdk deploy.