Response for the acknowledgement request is null.

Description

A request for Ack message has been sent at the background by the client; however, there is no response for the Ack message from the service side.

Initial message processing takes time. There are cases whereby the Ack message is not returned from the service side if the sending and receiving of the Ack message is performed at the background during the initial message processing.

Action

Contact the service for the cause.