Broken Verification Link: Double-check that the email template containing the verification link is configured correctly. Ensure the link itself is functional and not broken.
Expired Verification Link: The plugin allows you to set an expiration time for verification links. If the link expires before a user clicks on it, they will need to request a new verification email.
Email Blacklist: Verify that the email address used by the plugin to send emails is not blacklisted by any anti-spam services.