Once you campaign is running, it might have a queue of messages to be delivered. 

In our example, we setup campaign to send a first message an hour delay.

Once campaign is running, it will build a queue. Navigate to options dropdown 'Queue' or click on a number in 'Queue' column to the queue list.

Managing Queue

Use options dropdown to delete a message from queue, view a customer who is message is intended for or force to send that message immediately.