May be a duplicate of https://github.com/localstack/localstack/issues/988 but due to the age I will re raise.

I'm having issues when I throw an exception in a lambda - it isn't appearing on my dead letter queue. Is there something I am missing, I would like an sqs event exception to appear on the poison queue when an exception happens.

Below is the basic config:
 ````
    sqsclient.create_queue(QueueName = 'test-queue')
    sqsclient.create_queue(QueueName = 'test-queue-poison')

    lambda_client.create_function(
            FunctionName='MyFunction',
            Runtime='dotnetcore2.1',
            Role='role',
            Handler='Handler',
            Code=code,
	    DeadLetterConfig={'TargetArn': 'test-queue-poison-arn'})

     lambda_client.create_event_source_mapping(
		EventSourceArn='test-queue-arn',
		FunctionName='MyFunction',
		Enabled=True,
		BatchSize=100,
		StartingPosition='LATEST')
````

So when I raise a new (.net)exception within the lambda function no message is going to the dead letter queue. I can confirm that all is attached together OK as all other scenarios work, and the above code is pseudo-ish.
payload={'n': event_publisher.get_hash(lambda_name)})
        arn = func_arn(lambda_name)
        if arn in arn_to_lambda:
            return error_response('Function already exist: %s' %
                lambda_name, 409, error_type='ResourceConflictException')
        arn_to_lambda[arn] = func_details = LambdaFunction(arn)
        func_details.versions = {'$LATEST': {'RevisionId': str(uuid.uuid4())}}
        func_details.last_modified = isoformat_milliseconds(datetime.utcnow()) + '+0000'
        func_details.description = data.get('Description', '')
        func_details.handler = data['Handler']
        func_details.runtime = data['Runtime']
        func_details.envvars = data.get('Environment', {}).get('Variables', {})
        func_details.tags = data.get('Tags', {})
        func_details.timeout = data.get('Timeout', LAMBDA_DEFAULT_TIMEOUT)
        func_details.role = data['Role']
        func_details.memory_size = data.get('MemorySize')
        func_details.code = data['Code']
        result = set_function_code(func_details.code, lambda_name)
        if isinstance(result, Response):
            del arn_to_lambda[arn]
            return result
        
        func_details.code.pop('ZipFile', None)
        
        result.update(format_func_details(func_details))
        if data.get('Publish', False):
            result['Version'] = publish_new_function_version(arn)['Version']
        return jsonify(result or {})
    except Exception as e:
        arn_to_lambda.pop(arn, None)