I am planning doing a promotion.

I am wanting to do is when a Customer Purchase $50.00 or more they get a $15.00 Gift Voucher/Coupon they can either use it on the next purchase or give it to a Friend/Family Member.

My Question is,

If they want to give it to a Friend/Family member and they want to use the Gift Voucher/Coupon on their order how can they get a private code even they aren't registered in my store?