That kinda sucks... first time i see this problem with not marked as restricted humble gifts. Anyway - I am sorry that you cant activate it. the problem with humble gifts is - as soon as you claim it and open up (reveal) a steam key - gift link is useless. so i cant reroll it really. gift is claimed already... i try to find a solution maybe.

https://www.steamgifts.com/about/faq
What happens if I create a giveaway and the winner is unable to activate the gift in their region?
If you setup the giveaway with the appropriate region restrictions, and the winner was outside of those regions due to inaccurate information they provided, then you can request a new winner for the giveaway. If the giveaway did not have the correct region restrictions assigned to it, then one of three options are available.

You can acquire a replacement gift or key for the same game, which the winner is able to activate in their region.
You can accept the giveaway as being "Not Received" by the winner.
You can submit a ticket to have the giveaway deleted. In order for us to delete the giveaway, the winner will need to post a comment on the giveaway saying they agree to have it removed.
This is options from steamgifts rules for that situation.