Hey is there a problem if I put gift instead of key when creating a giveaway?

The only difference is that it doesn't require you to put a key/link. You can still send a key/link if you want, you just have to contact the winner manually instead of pressing the Send Key button that you would do if you had made it as a key/link to begin with.
It doesn't matter to the site or the rules how you send the game as long as it can be redeemed on Steam.

you can also select key and then put in the humble gift link.

ok thanks for letting me know.