The volume was not deleted because it would prevent a cloud snapshot operation from completing.
Make sure that you specified the correct volume. If so, wait for the cloud snapshot operation to complete, or cancel the cloud snapshot. Use the management GUI or the lsvolumebackupprogress command to monitor the progress of the cloud snapshot, or the rmvolumebackupgeneration command to cancel the cloud snapshot. Alternatively, specify the -cancelbackup parameter to force-delete the volume, canceling any active cloud snapshot operations on the volume.