cdk deploy fails due to stack using assets

README の手順から始め、cdk bootstrap aws://my_id/us_east_2 で使用されるアカウントとリージョンを、cdk deploy によって解決される環境と比較します。失敗を再現し、deploy が unknown-account/unknown-region を報告する理由を特定します。ドキュメントに記載されたデプロイが assets/bootstrap エラーなしで完了すれば完了です。

Following along the README I tried to deploy the template to an AWS-account after using

cdk bootstrap aws://my_id/us_east_2

which ended up in

 ⏳  Bootstrapping environment aws://my_id/us-east-2...
 ✅  Environment aws://my_id/us-east-2 bootstrapped (no changes).

but the cdk deploy ended up like this

❯ cdk deploy 
 ❌  lambdaapp failed: Error: This stack uses assets, so the toolkit stack must be deployed to the environment (Run "cdk bootstrap aws://unknown-account/unknown-region")
    at Object.addMetadataAssetsToManifest (/home/mhi/.nvm/versions/node/v14.16.0/lib/node_modules/aws-cdk/lib/assets.ts:27:11)
    at Object.deployStack (/home/mhi/.nvm/versions/node/v14.16.0/lib/node_modules/aws-cdk/lib/api/deploy-stack.ts:211:29)
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at CdkToolkit.deploy (/home/mhi/.nvm/versions/node/v14.16.0/lib/node_modules/aws-cdk/lib/cdk-toolkit.ts:180:24)
    at initCommandLine (/home/mhi/.nvm/versions/node/v14.16.0/lib/node_modules/aws-cdk/bin/cdk.ts:208:9)
This stack uses assets, so the toolkit stack must be deployed to the environment (Run "cdk bootstrap aws://unknown-account/unknown-region")

Is that due to a wrong region that was chosen? The AWS Account ID I took from the My Security Credentials section in the AWS Management Console.