If your library isn’t syncing across devices, here’s how to fix it step by step.

⚠️ Important: before doing anything, on the device that has the complete and up-to-date library, create a manual backup:

• Open Book Tracker > Settings > Backup & Restore > Create Backup.This ensures you won’t lose any data during the procedure.

Step 0 – Make sure iCloud is enabled

Before trying any troubleshooting steps, check that iCloud is enabled on your device and that Book Tracker has permission to use it.

• On iOS/iPadOS: go to Settings > [your name] > iCloud > Show All and ensure that Book Tracker is switched on.
• On macOS: open System Settings > [your name] > iCloud > iCloud Drive > Options, then verify that Book Tracker is selected.

If iCloud is disabled, the app won’t be able to sync your data.

Step 1 – Try to fix the device that is out of sync

1. On the device where the library is incomplete, open the Settings app.
2. Tap your Apple ID > iCloud.
3. Under Apps Using iCloud, tap Show All.
4. Find Book Tracker and turn it OFF.
5. Open Book Tracker: the library will clear.
6. Go back to Settings > iCloud > Show All and re-enable Book Tracker.
7. Open Book Tracker and wait for the library to download from iCloud.

If your data appears correctly, the issue is solved.

Step 2 – If the problem persists

If the out-of-sync device still doesn’t update, it usually means the device with the full library stopped uploading to iCloud.

To fix it:

1. On the device with the complete library, go to Settings > iCloud > Show All.
2. Turn Book Tracker OFF.
3. Open Book Tracker (the local library will clear).
4. Turn Book Tracker ON again.
5. Open Book Tracker and wait — the app will reconnect and start uploading the library to iCloud.

Step 3 – Restore the missing data

After this, Book Tracker should be connected to iCloud again. However, some books or changes may be missing (those not uploaded to iCloud before the issue).

To recover them:

1. On the same device where you created the manual backup at the beginning, open Settings > Backup & Restore.
2. Select the backup you created before.
3. Restore it.

Now your complete library will be back on the main device, and iCloud will sync it across all your devices.

CKErrorDomain 6 or 7

If you see an error like “CKErrorDomain 6” or “CKErrorDomain 7”, it usually means that Apple’s iCloud servers are temporarily slowing down or pausing the synchronization. This is a normal behavior designed to protect the service from overload.

CKErrorDomain 6 (“Service Unavailable”) appears when iCloud temporarily stops accepting new data uploads. This often happens when the app tries to sync a large amount of information at once, such as after importing a library from another app or restoring a backup. At first, iCloud allows the app to upload a large batch of records, but then it automatically applies a limit (called throttling) to slow down further requests. This helps prevent network congestion and ensures that the data is processed correctly on Apple’s servers. After some time, usually a few hours, iCloud automatically lifts the restriction and the synchronization resumes by itself.

CKErrorDomain 7 (“Request Rate Limited”) means that too many sync requests were sent in a short time. This can happen during large imports, backup restores, or when several devices are syncing simultaneously. The system temporarily delays further uploads to maintain stability.

If you encounter one of these errors, there’s no need to reset or reinstall the app. The best approach is simply to wait a few hours and keep the app open occasionally so that iCloud can automatically resume synchronization once the temporary limit has been lifted.

Extra tips

• Keep Book Tracker in the foreground and connected to Wi-Fi until syncing finishes.
• Disable Low Power Mode on iPhone/iPad to prevent interruptions.
• Large libraries may take several minutes to re-upload.

👉 Apple’s guide: If iCloud isn’t working.