Issues about incremental backup

While testing the incremental backup flow using REST API on RHV 4.4, I've found some issues.

When I sent "GET /vms/vm_id/backups/backup_id"
I could not find any attribute "to_checkpoint_id" when it showed "ready"
And no data for "GET /vms/vm_id/checkpoints"
Neither after "POST /vms/vm_id/backups/backup_id/finalize"

I've followed the guides on the oVirt website because I could not find any instructions about incremental backup in the RHV 4.4 documents.

Has the feature been implemented on RHV 4.4 ?

Thanks.

Best regards,

Min-Joon Kim.