You can customize the error messages that will be displayed in certain situations by providing a languageDictionary option. A full listing of available languageDictionary fields to customize can be found in the GitHub repository’s English Dictionary file for Lock. Below is an example of some customized error messages: 
// Examples of customized error messages in the languageDictionary option
var options = {
  languageDictionary: {
    error: {
      login: {
        "lock.invalid_email_password": "Custom message about invalid credentials",
        "lock.network": "Custom message indicating a network error and suggesting the user check connection",
        "lock.unauthorized": "Custom message about a failure of permissions",
        "too_many_attempts": "Custom message indicating the user has failed to login too many times."
      },
      signUp: {
        "invalid_password": "Custom message indicating a password was invalid",
        "user_exists": "Custom message indicating that a user already exists"
      }
    }
  }
};

// Initiating our Auth0Lock
var lock = new Auth0Lock(
  '{yourClientId}',
  '{yourDomain}',
  options
);

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Custom errors in Rules

If you are returning custom error codes from a rule or a custom database script, you can handle custom errors:
  • In your application’s redirect URL by reading the error and error_mesage query string parameters.
  • By redirecting the user back to your hosted pages with a custom error message and displaying the message with a flash message.

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Learn more