The issue cannot be unpublished

Unpublishing the articles first, or deleting the issue, when an issue with published articles cannot be unpublished.

Who uses it: Editor-in-chief, Catalogue editor, System administrator
Permission needed: Edit the profiles and issues of the journals in scope, Publish and unpublish catalogue records
In the panel: Issue Page

An issue cannot be unpublished while it has published articles. The notification reads "Unpublish the issue's published articles first." Unpublish the articles first, then unpublish the issue.

On the Catalogue → Publications screen, find the articles of the issue.
Select the articles and press Unpublish in the bulk action bar.
Write the reason and confirm the preview.
On the issue page, press Unpublish issue.
Write a reason of at least 5 characters and confirm.

The steps of the bulk action are in Bulk Actions. Unpublishing articles requires the permission to publish in the catalogue.

Removing the issue completely

If the issue will not be published again, you can delete it even while it is published. The deletion dialog either keeps the published articles in the catalogue as drafts or moves them to the trash. The steps are in Deleting a Journal Issue.