Cant center button on sm in Boostrap 4!

Im trying to use justify-content-center on row that surrounds the button i want to center on smaller screens ONLY but its not working, any idea what to do?

Hello there.

You have sent the boilerplate link, and not your own project. Please edit your post to include it.

Im unable to use Bootstrap in JSFiddle. How do i use it?

You have put the incorrect link in your original post. We are not able to help you, unless you give us the URL/code for your project.