Hey saw u apply there. I suggest checking out the FAQ in SG. Also there are 3 different types of GAs: Public(like this one), Group(Steam groups you join, where SG users can giveaways games here) and Invite only (you can enter via link). People usually win from the latter 2.

Group Giveaways require you to join the group with your 1 SG/Steam account. It should be the same one.
Alternate SG accounts are not allowed, as that would be unfair. So dont make an SG account from your alt. That will get you in trouble.

CD keys are often restricted. Check the packages on SteamDB: https://steamdb.info/app/1259420/subs/

CD-Keys are generated by Steam for and sold by the Publisher or Developer on non-Steam Stores.
They can restricted in multiple ways.
Generally they won't allow low-income countries to buy them cheap and then the keys be activated in other countries where the price may be higher.
That would mean loss of income forthe publisher.
It all depends on where you bought a key.
Even if the seller states it's region-free it could still be restricted. Plenty of 3rd party sites and sellersdon't give a damn.
Isthereanydeal.com lists official sellers.