MessagePublishReceiptListener is not getting the acknowledgement python API

class SolaceMessagePublishReceiptListener(MessagePublishReceiptListener):
    def __init__(self):
        self._publish_count = 0

    @property
    def get_publish_count(self):
        return self._publish_count

    def on_publish_receipt(self, publish_receipt: 'PublishReceipt'):
        with lock:
            self._publish_count += 1
            print(f"\tSOLACE -- \n", f"\tMessage: {publish_receipt.message}\n",
                  f"\tIs persisted: {publish_receipt.is_persisted}\n", f"\tTimestamp: {publish_receipt.time_stamp}\n",
                  f"\tException: {publish_receipt.exception}\n")
            if publish_receipt.user_context:
                print(f'\tUsercontext received: {publish_receipt.user_context.get_custom_message}')
                        

used the receipt listener by:

publisher= messaging_service.messaging_service\
            .create_persistent_message_publisher_builder().build()
publisher.start()
print('SOLACE -- PERSISTENT publisher started')

# adding the message recipient to the publisher
publish_receipt_listener = SolaceMessagePublishReceiptListener()
publisher.set_message_publish_receipt_listener(publish_receipt_listener)

messages published synchronously

publisher.publish_await_acknowledgement(outbound_message, topic, 2000)

However, after publishing the message successfully, we are not getting any acknowledgment from the listener.

Anyone tried this receipt listener in the solacePubSub python API?