In the Vault, first open Contacts → Mobile & app connections, create a Contacts-only client password for the device, and copy it when displayed.
Then open Settings → Apps → Contacts → Contacts Accounts → Add Account → Other → Add CardDAV Account on current iOS and iPadOS versions.
- Server:
dav.lightdrive.one - Username: your full LightDrive email address
- Password: the Contacts-only client password created for this device
Keep SSL enabled. If discovery does not find the address book, use the complete path https://dav.lightdrive.one/USERNAME/contacts/. Your main Vault password, Vault app passwords, and Email-only passwords do not work for CardDAV.
Set LightDrive as the default contacts account if you want new contacts created on the device to be stored there automatically.