most of the time when keys show up as invalid it's often a copying error or an issue with the browser.
i've quite literally had keys that were so finicky. User A couldn't get it to work so i gave them a new code. I gave the (supposedly unworking) code to another user and they had 0 issues :/
have the people who you're giving keys to make sure they aren't accidentally copying spaces or extra characters (i.e., if you give them codes "in quotes" or [in brackets] make sure they aren't copying those too!). alternatively, see if you can get the code to work and make their account for them with a temporary password
i have done that way too many times at work
if the problem persists, definitely file a ticket because admin tend to respond to that much quicker.
if you need more codes because the ones you have aren't working, hmu because i have plenty.