Actually seeing it can sometimes be surprisingly hard even if you are told exactly where to look.

The simplest thing to do might be to copy the variable name from its declaration, and paste it over the complaint. Maybe it was an 'rn' vs 'm' or some arcane magic the cat typed in and you just can't see it, but either way copy-paste will fix it.

If such things continue to be an issue, I recommend changing the editor and/or console to either increase the font size or use a different font with more distinct characters.