This is a restricted gift which can only be redeemed in these countries: Armenia, Azerbaijan, Belarus, Georgia, Kyrgyzstan, Kazakhstan, Moldova, Republic of, Tajikistan, Turkmenistan, Uzbekistan, Ukraine, Russian Federation

This gift cannot be added to inventory, only to library

Go to https://store.steampowered.com/login and log into your Steam account
Click on the link you received from the transaction
The link will take you to a screen with two options to Accept gift or Decline gift