If you’ve enabled Two-Factor Authentication for your Vivaldi account, then you need to use an app password when adding your account to mail and calendar clients, such as Vivaldi Mail and Vivaldi Calendar.

To generate an app password:

1. Log in to your Vivaldi account on Vivaldi.net and go to the profile.
2. Go to the Two-Factor Authentication management page and verify your identity with the login password.
3. If you have at least one 2FA method set up, you’ll see an option to create App Passwords, go to that page.
4. Select the type of app (mail, calendar, or both) you want to create the password for.
5. Give it a name, so you’ll recognize which apps and clients you’ve generated passwords for.
6. Copy the password, enter it on the login page of the client, and store the password in a safe location as this is the only time the password will be shown to you.