Currently, the function of activating gift codes on iOS devices is limited due to the restrictions from the mobile platform, so activation of gift codes directly in the game is not available.
However, you have the option to activate a gift code via a link. To do that, add the desired gift code to the link after the "=" sign: playkot://adventures?gift=
Close the game completely by unloading it from your device memory. Copy the link and paste it into your browser address bar or "Notes" on your device, then follow it from there.
More information on gift codes is available here.