In my band, the lead singer also plays the Guitar Hero III Guitar. But when I try to add that to the credits and roles, it doesn’t work. Yes, he really does.
Are you trying to add "Guitar Hero III Guitar" verbatim? That, of course, won't work. You need to select a valid guitar credit role out of this list: https://www.discogs.sie.com/help/creditslist and enter the verbatim credit in brackets: "Credit Role [Credit Role Specification]".
