How to Fix UnlockTool Invalid HostID (-21) Error – Get Activation FAIL

If you get the error “ERROR: Could not connect to lockdownd: Invalid HostID (-21) FAIL” in UnlockTool when clicking Get Activation, this guide provides a simple troubleshooting method you can try.

The problem can be related to the Windows Lockdown folder and stored device pairing data. Removing the existing files from this folder can force the related service to create fresh pairing information.

UnlockTool Invalid HostID (-21) Error

This issue may appear when UnlockTool cannot properly communicate with the Apple device service and reports an invalid HostID. The error may look similar to:

ERROR: Could not connect to lockdownd: Invalid HostID (-21) FAIL

Before starting, close UnlockTool and other Apple device management tools such as 3uTools.

How to Fix Invalid HostID (-21) in UnlockTool

Step 1 – Open Windows Search

Click the Windows Search box or search icon located on the lower-left side of the Windows taskbar.

Step 2 – Open the Windows Lockdown Folder

Enter the following path into Windows Search or the File Explorer address bar:

Press Enter and Windows will open the Apple Lockdown folder.

Step 3 – Delete the Lockdown Files

Inside the Lockdown folder, you may find files created from previous Apple device pairing sessions.

Delete the files inside this folder. Do not delete the Lockdown folder itself.

After deleting the files, reconnect the Apple device if necessary.

Step 4 – Try Get Activation Again

After cleaning the Lockdown files:

1. Close and reopen UnlockTool.
2. Connect the Apple device again.
3. Open the activation function.
4. Click Get Activation again.

If the issue was caused by corrupted or outdated Lockdown pairing data, the tool may now be able to establish a fresh connection.

Conclusion

The Invalid HostID (-21) FAIL error in UnlockTool can sometimes be resolved by clearing the files stored in:

%ProgramData%\Apple\Lockdown\

After removing the existing files, restart UnlockTool and try Get Activation again. If the error continues, check the Apple drivers, device connection, USB cable, and any other Apple-related service running on Windows.

Important Note

Deleting Lockdown pairing files can remove existing pairing records, so you may need to reconnect and trust/pair the device again. Only perform these steps on devices you are authorized to service.