'GT legends" should not register in steam gift?

What?

Huh?

the moderator stated that It is not allowed to giveaway exploited games, so your giveaway is removed

GT Legends has been removed by Kaitlyn, a moderator. Points have been refunded to those that entered. Sorry for the inconvenience.
Reason: Exploited Key
Notes: Keys that take advantage of promotions using methods that were never intended are not allowed to be given away on SteamGifts. Please refer to our FAQ to learn more.

what i got from it.
why didn't my giveaway of GT legends register. (have no idea what that part means)
A mod deleted the giveaway and some people already entered the giveaway.
then again, i may be completely wrong with the translation