A queue activity allows for the execution of an offer following its upstream queue listener’s receipt of data via a JSON package arriving on the listener queue (and the optional customization of the content therein based on the data thus received, using parameter attributes).
You can only attach a queue activity to a queue listener. A queue activity cannot be attached to more than one queue listener. You cannot add a queue activity downstream from another queue activity. You also cannot add any other activitites downstream from a queue activity.