I'm trying to add external links to the Design System we're going to be using, which is Material UI. Its URL is https://material-ui.com/
Every time I try, I get an error message saying to enter a valid URL. I tried copy/paste and manually typing, and it seems that as soon as I type the hyphen, it causes the error.
This is pretty major, since I need these URLs to launch my DSM.
Links to screenshots
no error message: https://gyazo.com/5db4294835503bb693f0488fcd8e2a47