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The key activated this package and when you check on SteamDB you can see the list of countries that it can't be activate in.
I have a browser extension that adds a link to the package on SteamDB (either the one from SteamDB themselves, or Augmented Steam, I can never remember which one added the link) whenever I activate a key on the Steam website, but that's not much help until you actually activate the key...

The best source of region lock info are SensualShakti's excellent bundle threads in the deals discussions here on SteamGifts. For example here is the one for the Humble Double Fine 20th Anniversary Bundle.
Look for the ⚠️Region lock⚠️ section near the top of the post.