Zadara Compute provides two different types of Snapshot, Volume Snapshots and VM Snapshots. VM Snapshots create Volume Snapshots of all Volumes attached to the VM, where the underlying Volume Snapshots are managed by the top-level VM Snapshot.
These managed Volume Snapshots cannot be deleted directly. Attempting to do so will result in a Snapshot deletion failed, indicating that the Snapshot is referenced by vm-snapshot:
It will provide the ID of the VM Snapshot which manages the Volume Snapshot. You can also see which VM Snapshot manages a Volume Snapshot in the description field of said Volume Snapshot:
Deleting a VM Snapshot will delete all the Volume Snapshots it manages.