I followed the video and created a string flag and copy and pasted the code yet the name is invisible. Can someone please help me? I want to be able to allow the player to use their own custom name.

Did you copy the embedded flag html from our blog post?? The one from the blog post doesn't work, you have to use the one I pinned in the youtube video top comments. 

Anyway I fixed it, 

This is what you had before: <span data-flag=”mcName”></span>
when you encode it the engine reads it as & rdquo;

This is the correct one: <span data-flag="mcName"></span>
when you encode it the engine reads it as & quot;

To make sure you're using the right quotations next time, use this website to encode/decode the HTML to make sure you're using the right quotations: https://www.web2generators.com/html-based-tools/online-html-entities-encoder-and-decoder