Why are my prospects showing as unavailable for a marketing campaign?

Why can't I add my prospects to a marketing campaign?

Prospects can only be in one marketing campaign at a time. However, if your prospects are not currently in a marketing campaign and still showing as unavailable, it may be because they are in a Marketing Delay.

Even if they've been in a completed or canceled campaign, you may have already set the marketing delay for the records within those campaigns. So those records must wait until the delay days have passed before they can enter a new campaign.