I enabled third-party cookies in my browser, but I am still getting an error message to enable third party cookies! Why?

When this happens it is usually the result of a privacy extension or ad blocker. You'll just need to add b4g.baydin.com and mail.google.com to the extension's trusted (or accepted/etc.) list. Then reload Gmail and give it another try. 

If the issue persists, please email support@baydin.com.