To delete a Matter, you must “close” the Matter first.
On the Matter Dashboard, go to the matter click Settings and then “Close”.
When you close the Matter, you will be automatically redirected to the Closed matters page. You can delete the Matter by clicking on the trash bin in the matter row.
Deletion will also ask for your confirmation, and upon confirmation, all Matter files and Office 365 group will be permanently deleted and cannot be restored.
It's not possible to delete Matters with existing unpaid invoices. If there are unpaid invoices on a closed Matter, the delete button for them is disabled (grayed out).