Error sending email: Error: Missing credentials for "PLAIN"

 The error "Missing credentials for 'PLAIN'" usually occurs when there is an issue with the authentication credentials provided. To resolve this error, you can try the following steps:

1. Double-check that the email address and password used for authentication are correct. Make sure there are no typos or mistakes in the credentials.

2. If you are using 2-step verification for your Gmail account, you need to generate an "App Password" specifically for this application. Follow these steps to generate an App Password:

   - Go to your Google Account settings.

   - Navigate to the "Security" section.

   - Look for the "App Passwords" or "Less secure app access" option (the exact wording might vary).

   - Generate a new App Password and use it in your code instead of your account password.

3. If you have enabled any additional security measures for your Gmail account, such as two-factor authentication or application-specific password requirements, make sure you have properly configured your account and the code accordingly.

By ensuring that the correct credentials are provided and any additional security measures are properly configured, you should be able to resolve the "Missing credentials for 'PLAIN'" error and successfully send emails.