There are a few reasons you could be seeing a password error on attempting to sync your contacts.
- Your username/password is wrong. Check caps lock isn't on, and for common visual errors like mistaking a 0 (zero) for an O (capital o), or a 1 (one) for an l (lowercase letter L).
- You used your 2FA credentials or your account password. You need to use an app password for CalDAV or CardDAV access.
- When syncing with an external service (not just to your device), and your external account has two-factor authentication enabled, you need to generate an application password.
Here are instructions for generating application passwords for popular sites you might be syncing your information with: