macOS Error: An unknown authentication error happened

If you receive such an error, try following these steps:

1. Option + Command + Esc to force quit the NordVPN application.
2. Click on Launchpad and in a search field type "Keychain Access".
   
   
    
3. Select the "login" entry in the keychain (top left corner of the window).
   
   
    
4. Right-click on the "login" keychain and choose Lock Keychain "login".
5. Then try unlocking it again.
6. You might need to enter your Mac login password afterward.
7. Relaunch the NordVPN application and try logging in again.

If you cannot unlock the keychain as recommended in the method above, try doing that over the terminal:

1. Open Launchpad and type "Terminal" in a search field.
2. After opening the terminal enter the following command:
   security lock-keychain
    
3. Run this single-line command to unlock the keychain:
   security unlock-keychain
    
4. Enter your macOS password and press the return button.
   
   
    
5. Try logging in again.