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.
queue_url = req_data.get('QueueUrl')
        if queue_url:
            return queue_url[0]
        url = config.TEST_SQS_URL
        if headers.get('Host'):
            url = 'http%s://%s' % ('s' if config.USE_SSL else '', headers['Host'])
        queue_url = '%s%s' % (url, path.partition('?')[0])
        return queue_url
def get_external_port(headers, request_handler):
    host = headers.get('Host', '')
    if ':' in host:
        return int(host.split(':')[1])
    
    
    
    return request_handler.proxy.port
UPDATE_SQS = ProxyListenerSQS()