Lambda destination not being triggered on Lambda error

I have a Cloudformation stack which connects two Lambdas together via a Lambda destination config and an SQS queue.

The idea is that ErrorsFunction is fired when there is an error in HelloAddFunction.

This stack deploys fine, and HelloAddFunction works fine when I invoke it with some integer values.

I can see an error in HelloAddFunction when I invoke it with non- integer values, but no corresponding error seems to be received by ErrorsFunction.

The binding of ErrorsFunction to ErrorsQueue seems to be working - if I push a message onto ErrorsQueue via the console, it's received by ErrorsFunction.

So it feels like the Lambda destination config is somehow not working.

What am I missing here ?

TIA

AWSTemplateFormatVersion: '2010-09-09'
Outputs: {}
Parameters:
  AppName:
    Type: String
  MemorySizeSmall:
    Default: 512
    Type: Number
  RuntimeVersion:
    Default: '3.8'
    Type: String
  TimeoutShort:
    Default: 5
    Type: Number
Resources:
  HelloAddEventConfig:
    Properties:
      DestinationConfig:
        OnFailure:
          Destination:
            Fn::GetAtt:
            - ErrorsQueue
            - Arn
      FunctionName:
        Ref: HelloAddFunction
      MaximumRetryAttempts: 0
      Qualifier: $LATEST
    Type: AWS::Lambda::EventInvokeConfig
  HelloAddFunction:
    Properties:
      Code:      
        ZipFile: |
          def handler(event, context):
            x, y = int(event["x"]), int(event["y"])
            return x+y     
      Handler: index.handler
      MemorySize:
        Ref: MemorySizeSmall
      Role:
        Fn::GetAtt:
        - HelloAddRole
        - Arn
      Runtime:
        Fn::Sub: python${RuntimeVersion}
      Timeout:
        Ref: TimeoutShort
    Type: AWS::Lambda::Function
  HelloAddRole:
    Properties:
      AssumeRolePolicyDocument:
        Statement:
        - Action: sts:AssumeRole
          Effect: Allow
          Principal:
            Service: lambda.amazonaws.com
        Version: '2012-10-17'
      Policies:
      - PolicyDocument:
          Statement:
          - Action: logs:*
            Effect: Allow
            Resource: '*'
          - Action: sqs:*
            Effect: Allow
            Resource: '*'
          Version: '2012-10-17'
        PolicyName:
          Fn::Sub: hello-add-role-policy-${AWS::StackName}
    Type: AWS::IAM::Role
  ErrorsFunction:
    Properties:
      Code:
        ZipFile: |
          def handler(event, context):
            print (event)
      Handler: index.handler
      MemorySize:
        Ref: MemorySizeSmall
      Role:
        Fn::GetAtt:
        - ErrorsRole
        - Arn
      Runtime:
        Fn::Sub: python${RuntimeVersion}
      Timeout:
        Ref: TimeoutShort
    Type: AWS::Lambda::Function
  ErrorsQueue:
    Properties: {}
    Type: AWS::SQS::Queue
  ErrorsQueueBinding:
    Properties:
      EventSourceArn:
        Fn::GetAtt:
        - ErrorsQueue
        - Arn
      FunctionName:
        Ref: ErrorsFunction
    Type: AWS::Lambda::EventSourceMapping
  ErrorsRole:
    Properties:
      AssumeRolePolicyDocument:
        Statement:
        - Action: sts:AssumeRole
          Effect: Allow
          Principal:
            Service: lambda.amazonaws.com
        Version: '2012-10-17'
      Policies:
      - PolicyDocument:
          Statement:
          - Action: logs:*
            Effect: Allow
            Resource: '*'
          - Action: sqs:*
            Effect: Allow
            Resource: '*'
          Version: '2012-10-17'
        PolicyName:
          Fn::Sub: errors-role-policy-${AWS::StackName}
    Type: AWS::IAM::Role