If an "agent user" publishes a campaign and needs to cancel, or if there's an unspent balance on a campaign that has finished, by "archiving" the campaign the balance will be assigned to the agent user as an ad credit.
If an "admin user" publishes a campaign on behalf of an agent - only the admin user will be able to access the ad credit.
Ad credits can be selected within the campaign setup on the page where you set the campaign budget & duration.
If you have used an ad credit to pay for a campaign (or part payment) and then you archive this campaign, please notify [email protected] as one of the team will be able to add this back in manually.