CKShare - Failed to modify some records error - CloudKit

I'm trying to share a record with other users in CloudKit but I keep getting an error. When I tap one of the items/records on the table I'm presented with the UICloudSharingController and I can see the iMessage app icon, but when I tap on it I get an error and the UICloudSharingController disappears, the funny thing is that even after the error I can still continue using the app.

Here is what I have.

Code

var items = [CKRecord]()
var itemName: String?

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let item = items[indexPath.row]

    let share = CKShare(rootRecord: item)

    if let itemName = item.object(forKey: "name") as? String {
        self.itemName = item.object(forKey: "name") as? String
        share[CKShareTitleKey] = "Sharing \(itemName)" as CKRecordValue?
    } else {
        share[CKShareTitleKey] = "" as CKRecordValue?
        self.itemName = "item"
    }
    share[CKShareTypeKey] = "bundle.Identifier.Here" as CKRecordValue
    prepareToShare(share: share, record: item)
}


private func prepareToShare(share: CKShare, record: CKRecord){

    let sharingViewController = UICloudSharingController(preparationHandler: {(UICloudSharingController, handler: @escaping (CKShare?, CKContainer?, Error?) -> Void) in

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

        modRecordsList.modifyRecordsCompletionBlock = {
            (record, recordID, error) in

            handler(share, CKContainer.default(), error)
        }
        CKContainer.default().privateCloudDatabase.add(modRecordsList)
    })

    sharingViewController.delegate = self

    sharingViewController.availablePermissions = [.allowPrivate]
    self.navigationController?.present(sharingViewController, animated:true, completion:nil)
}



// Delegate Methods:
func cloudSharingControllerDidSaveShare(_ csc: UICloudSharingController) {
    print("saved successfully")
}
func cloudSharingController(_ csc: UICloudSharingController, failedToSaveShareWithError error: Error) {
    print("failed to save: \(error.localizedDescription)")// the error is generated in this method
}
func itemThumbnailData(for csc: UICloudSharingController) -> Data? {
    return nil //You can set a hero image in your share sheet. Nil uses the default.
}
func itemTitle(for csc: UICloudSharingController) -> String? {
    return self.itemName
}

ERROR

Failed to modify some records

Here is what I see...

Any idea what could be wrong?

EDIT:

By the way, the error is generated in the cloudSharingController failedToSaveShareWithError method.

Looks like you're trying to share in the default zone which isn't allowed. From the docs here

Sharing is only supported in zones with the CKRecordZoneCapabilitySharing capability. The default zone does not support sharing.

So you should set up a custom zone in your private database, and save your share and records there.