When you turn on the authentication code the receiver of the note will be asked an authorization code to read the note.
The sender of the note needs to send this code to the receiver through a different medium as how the link was shared.
This is a extra security measure to make sure that only the receiver can read the note.
You could use the following mediums to send the authorization code:
- Phone Call
- SMS message
- Instant Message (Signal, Telegram, Whatsapp, etc...)
- In person
- Post
- Post pigeon