Hey @SIAC, welcome to the Seller Community! I can see that this is your first post with us!
Are you currently using Square Online to host your website, or are you building your website using Square's API?
If you are using Square Online, the 3DS feature is already built into our integration, so you should be able to accept payments immediately.
If you are using our API, I'd recommend visiting our Developers Forum to get in touch with one of our developers to get in touch with a developer, as they would be better equipped on providing guidance in adding a 3D Secure Rule to your website.
If neither of these apply, could you provide a little more information as to where you are trying to apply the 3D Secure Rule? This would allow me to better help you. Thanks!
