Why does my stack deletion fail because of an error that occurs when deleting a custom resource?

Question

My custom resource is configured as follows:

```
Resources:
    SecretTagValCreation:
      Type: Custom::SecretTagValCreation
      Properties:
        ServiceToken: arn:aws:lambda:us-east-2:ACCOUNT_NUMBER:function:ReturnSecretToCFNForEC2
        Region: !Ref "AWS::Region"
        Env: !Ref 'EnvTagValue'
        ProjID: !Ref 'ProjIDTagValue'
        Dept: !Ref 'DepTagValue'
        Owner: !Ref 'OwnerTagValue'
        StackID: !Ref 'AWS::StackId'
        StackName: !Ref 'AWS::StackName'
```

I have the AWS CloudFormation stack created in one account, and an AWS Lambda function created in a different account. My code works, and the Lambda function can be invoked by the CloudFormation role. 
However, I can't delete my stacks because the custom resource doesn't get deleted during stack creation. The status of the stack is "DELETE_FAILED" or "ROLLBACK_FAILED" (if there is an error with stack). If I retain the custom resource and try deleting the stack again, then the stack gets deleted. However, this is not ideal. How do I delete the resources properly?

Accepted Answer

This issue occurs under one or more of the following conditions:
* You don't send a response.
* An issue occurs during your handler's cleanup.

Check if you've implemented the delete event in your Custom Resource (`event['RequestType'] == 'Delete'`).

Why does my stack deletion fail because of an error that occurs when deleting a custom resource?

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