People should be able to refer a friend if they already own the game.
The friend referral code should not be required at checkout and should be applicable by people who already own the game. Requiring new people to buy new copies of the game to count as being referred is a massive fuck you to people who've already been supporting the game and encouraging other people to support the game way earlier in development. My friends and I for example have already referred as many friends to the game as we'll ever be able to do and that involved supporting the game way before it was showing progress. It's essentially a punishment to people who convinced their friend to buy the game before this point. It also disproportionately benefits people with large clans who will easily buy alternative copies of the game in order to refer to each other.