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.
if not msg:
        msg = 'The resource you requested does not exist.'
        if ref:
            msg = '%s not found: %s' % ('Function' if ':function:' in ref else 'Resource', ref)
    return error_response(msg, 404, error_type='ResourceNotFoundException')
@app.before_request
def before_request():
    
    transfer_encoding = request.headers.get('Transfer-Encoding', '').lower()
    if transfer_encoding == 'chunked':
        request.environ['wsgi.input_terminated'] = True
@app.route('%s/functions' % PATH_ROOT, methods=['POST'])
def create_function():
    """ Create new function
        ---
        operationId: 'createFunction'
        parameters:
            - name: 'request'
              in: body
    """
    arn = 'n/a'
    try:
        data = json.loads(to_str(request.data))
        lambda_name = data['FunctionName']
        event_publisher.fire_event(event_publisher.EVENT_LAMBDA_CREATE_FUNC,