Five hostnames, as they would appear in a browser's address bar or in a link somebody sent you.
One of them is not the name it looks like. It is a different name that renders identically, because one of its letters is from another alphabet — and no amount of looking carefully will tell you which, because looking carefully is precisely what this defeats. That is the lesson, not the puzzle.
The tool below reports which lines contain a character outside ASCII and names the codepoint. That identifies the line. Turning the name into the form a certificate or a DNS zone would show you is the other half, and the hint explains how.
Submit the ASCII-compatible form of the odd name: skrd{xn--...}.