Post the key and i will tell u. But really probably desura

Mail him that the key is not working on steam

Perhaps instead you could post like a possible format of the key, similar to the page when you are inputting a key to Steam

Might be a stupid question, but: have you actually tried activating it?

Try to get in contact with him but if you really can't reach him, after the 7-day waiting period just mark the gift as not received. I'm guessing you could also contact the mods about it.

Also, make sure you wrote the key correctly on Steam, without spaces at the beginning or end. I once sent a key to someone and he kept saying that he got an invalid key message, but on my account it simply said that I already owned the game. He finally managed to get it working after a few more tries.

He probably bought one of the older packs on amazon, which do not activate on steam. Basically, it's useless for you, as you would also need the amazon download from his library. I'd say, let him know he made a mistake and mark it as not received, I guess.

Don't call out submitters. And contact steamgifts support

Have you tried activating it on desura?

It's from amazon and he should have received a key for steam along with the non steam key as well.
Try to contact the gifter.

I bought the bundle from amazon and they provide you with a key that I have no idea where to redeem, but they also sent me a steam redeemable key in mail. He either got one on his mail or it's on his amazon page.

Edit : Also please remove the link from the topic description.

Tell him to check his E-mail, the steam keys were sent there; those are not steam keys in his Games Library section on Amazon