This is region restricted. From Humble I think.

This key is only available in the countries listed below. If the person you're gifting this to doesn't live in one of them, Steam might prevent the key from being redeemed.
Europe AD AI AL AT AX BA BE BG BM BQ CH CS CY CZ DE DK EE ES FI FK FO FR GB GF GG GI GP GR GS HR HU IE IO IS IT JE KY LI LT LU LV MC MK MQ MS MT NL NO PL PN PT RE RO SE SH SI SJ SK SM TC TR VA VG YT