{
  canUse: boolean;
  message: string;
  reason?: string;
  coupon?: CouponValidation | null;
}

async function applyCoupon(code, document) {
  const result = await storefront.coupons.validate({ code, document });

  if (!result.canUse) {
    alert(result.message);
    return;
  }

  // aplicar no carrinho / checkout
}