Not sure how to redeem this key

Or indiegala. But its diffrent with an acceptable gift link rather then forcing winner to do extra steps to get the game with a code to diffrent site.

Generally, codes like that can be useful in that they often give both DRM-Free and Steam copies of a game [Groupees gifting works that way, for example, as do many Gamersgate and some Humble Store purchases]. So long as the winner doesn't have to complete special (promotional, commercial, etc) tasks to get a game-

You cannot ask users to perform any special action in order for their entry to be considered valid, such as liking a Facebook page, or following a Twitter account.

-then you can give any kind of code you please. Of course, you're still responsible for making sure the winner is able to acquire the actual game, and the more steps involved in that process, generally the more hassle there is for everyone involved. Nevertheless, it can often be to the benefit of the winner to get the actual store code- though that should really be explained in detail by the GA creator, and the winner should have the option to comment that they're not interested in the extra steps.

Gift links are the same thing- they usually offer some sort of account linking, support right transfer, or similar element to them; ie, a secondary benefit. If you then tell the GA creator "I can't access e-mail,", then as I understand staff's take on delivery rules, the GA creator still has the obligation (if they don't want to be stuck with a Not Received) to then send the gift link to their own e-mail, pop it open, grab the key, and give you that.

Now, all that said, that doesn't actually seem to be the case here- if the site linked above is actually the one being used, the validation code in question seems to just be a confirmation code to send to the account/e-mail already on file. As indicated by xMisiu, it's likely the GA creator just missed some steps.

It's also considered rude to contact someone on Steam if they haven't explicitly told you you should, and if you haven't tried to contact them through the site first (and waited a suitable amount of time after that- at the least, it's generally best not to contact on Steam [without an invitation to do so] before the seven day period is over).
As a rule of thumb there's a certain expectation of being blocked or ignored on Steam if you poke there first (for example, I personally never look at Steam invites unless told to do so, and automatically assume every other invite on there is from a bot/scammer by default even when I do look).

If you've been blacklisted, support can sometimes contact the GA creator for you, to update them of the situation. Putting in an Other ticket also lets you leave staff updates on the giveaway, if being blacklisted prevents you from leaving such in giveaway comments. If you're not blacklisted, then using the giveaway comments is generally the most preferable and reliable course of action.