It is a number or a code that can be used for specific occasions, given by the SON team, and will give you great packs and items.
When codes are available, players will be notified from the game's social media platforms or in-game announcements.

Strike Of Nations on Facebook:
www.facebook.com/strikeofnations

Strike Of Nations on Twitter:
twitter.com/NationsStrike

Strike Of Nations on Instagram:
www.instagram.com/strikeofnations