To pause a campaign, navigate to the campaign overview. Please note that campaigns cannot be unpublished and making the campaign unavailable to participants should be done by pausing it.
Click the three dots and select 'pause campaign'.
Remember to check the live URL and confirm that the campaign has been paused.
If needed, you can modify the message a user sees when they access the campaign.
You can modify in-game messages in the advanced tab, as displayed below: