Using Ckcloud Kit to Share Private Records

I believe the error message is telling you need to save the share and root record at the same time.

let modifyRecordsOperation = CKModifyRecordsOperation( recordsToSave: [record, share], recordIDsToDelete: nil)

You should do this operation in the completion handler of the sharingController.

sharingController = UICloudSharingController {
                        controller, preparationCompletionHandler in

Edit: Your code would look something like this not tested code:

@IBAction func testPress(_ sender: Any) {
    let privatedatabase = CKContainer.default().privateCloudDatabase
    let newZoneName = UUID().uuidString
    let recordZone = CKRecordZone(zoneName: "ShareZone")

    privatedatabase.save(recordZone) {  savedRecordZone, error in

        if let error = error {
            print("\(error.localizedDescription).")
        } else if let savedRecordZone = savedRecordZone {
            print("\(error.localizedDescription).")

            let rootRecord = CKRecord(recordType: "RootRecord", zoneID: savedRecordZone.zoneID)
            rootRecord["Name"] = "Test" as CKRecordValue?

            privatedatabase.save(rootRecord) { record, error in
                if let error = error {
                    print("\(error.localizedDescription).")
                } else if let record = record {
                    print("successfully added rootRecord to cloud.")
                    self.shareTest( rootRecord: record)
                }
            }
        }
    }
}

func shareTest(rootRecord:CKRecord) {

    let ckContainer = CKContainer.default()
    let shareRecord = CKShare(rootRecord: rootRecord)

    let sharingController =  UICloudSharingController { controller, preparationCompletionHandler in

        let share = CKShare(rootRecord: record)
        share[CKShareTitleKey] = "Share Title" as CKRecordValue
        share.publicPermission = .none

        let modifyRecordsOperation = CKModifyRecordsOperation( recordsToSave: [rootRecord, share], recordIDsToDelete: nil)
        modifyRecordsOperation.timeoutIntervalForRequest = 10
        modifyRecordsOperation.timeoutIntervalForResource = 10

        modifyRecordsOperation.modifyRecordsCompletionBlock = { records, recordIDs, error in

            if let error = error {
                print(error.localizedDescription)
            }
            if let records = records {
                print("Share and Root records saved successfully")
            }
            preparationCompletionHandler(share, CKContainer(identifier: ckContainerID ), error)
        }

        myCloudDatabase.add(modifyRecordsOperation)
    }
    if let sharingController = sharingController {
        sharingController.availablePermissions = [.allowReadOnly, .allowReadWrite, .allowPrivate]
        sharingController.popoverPresentationController?.sourceView = sender
        sharingController.delegate = self
        self.present(sharingController, animated: true)
    }
}

// MARK: UICloudSharingControllerDelegate
// --------------------------------------
func cloudSharingController(_ csc: UICloudSharingController, failedToSaveShareWithError error: Error) {
    print("Failed to share to cloud: \(error)")
}
func itemTitle(for csc: UICloudSharingController) -> String? {
    return "Please join rootRecord share."
}
func cloudSharingControllerDidStopSharing(_ csc: UICloudSharingController) {
    print("Cloudkit stopped sharing")
}
func cloudSharingControllerDidSaveShare(_ csc: UICloudSharingController) {
    print("Cloudkit started sharing rootRecord")
}