Why did my backup job fail with 'snapshot-quota-reached' event type?

You receive an event notification with the event type 'snapshot-quota-reached'.

Your backup snapshot could not be created because you already have as many snapshots as you can. You can have 750 snapshots of first-generation storage volumes and 512 snapshots of second-generation storage volumes.

Delete unnecessary snapshots. Review and update your retention policy in the backup plan to make sure that you keep only the snapshots that you need.