Coupon Design and Constraints

About This Article

Coupons issued through point conversion have constraints to prevent fraudulent use. This article explains coupon specifications and their design rationale.

Basic Coupon Specifications

Characteristics of Issued Coupons

Item	Specification	Reason
Discount type	Fixed amount discount	Points = amount is easy to understand
Discount amount	Same as points used	Clear 1pt = 1 yen rate
Usage count	Once only	Points are consumed only once
User	Customer who requested issuance only	Prevent transfer to others
Validity	1 year from issuance	Provide sufficient time
Minimum purchase	None	Prioritize ease of use

Discount type

SpecificationFixed amount discount

ReasonPoints = amount is easy to understand

Discount amount

SpecificationSame as points used

ReasonClear 1pt = 1 yen rate

Usage count

SpecificationOnce only

ReasonPoints are consumed only once

User

SpecificationCustomer who requested issuance only

ReasonPrevent transfer to others

Validity

Specification1 year from issuance

ReasonProvide sufficient time

Minimum purchase

SpecificationNone

ReasonPrioritize ease of use

Coupon Code Format

Format: [Last 5 digits of customer ID]-[Random 6 characters]-[Point amount] Example: 70934-AB12CD-500

Part	Example	Meaning
Last 5 digits of customer ID	70934	Whose coupon
Random 6 characters	AB12CD	Prevent duplicates (multiple issuance per customer possible)
Point amount	500	How much discount

Last 5 digits of customer ID

Example70934

MeaningWhose coupon

Random 6 characters

ExampleAB12CD

MeaningPrevent duplicates (multiple issuance per customer possible)

Point amount

Example500

MeaningHow much discount

Benefits: Content visible from code, no duplicates, easy inquiry handling, difficult to generate fake codes

Constraint Details

Usage Count Limitation

At point conversion: 500pt consumed → 500 yen coupon issued

Customer-Specific Constraint

Shopify coupon settings:

customer_selection: "specific"
prerequisite_customer_ids: ["12345"]

Effect	Details
Usage restriction	Only customer 12345 can use this code
Leak protection	Others can't use even if code is leaked
Sharing prevention	Sharing within family also not possible

Usage restriction

DetailsOnly customer 12345 can use this code

Leak protection

DetailsOthers can't use even if code is leaked

Sharing prevention

DetailsSharing within family also not possible

Verification Flow

Customer enters code

Enter coupon code on checkout screen

Shopify checks

Is code valid? → Yes / Is this customer eligible? → Check customer ID

Result

Match → Apply discount / Mismatch → "This code cannot be used"

Validity Period Design

Expired handling: Expired coupon → Cannot use, Consumed points → Not returned, Advance reminder → Under consideration

Fraud Prevention Measures

Anticipated Fraud and Countermeasures

Fraud Pattern	Countermeasure
Code guessing	Random 6 characters makes guessing difficult
Code sharing	Customer-specific limits users
Multiple uses	Once-only limits usage
Use after expiration	Auto-invalidated by Shopify
Converting more than balance	Always check balance before conversion

Code guessing

CountermeasureRandom 6 characters makes guessing difficult

Code sharing

CountermeasureCustomer-specific limits users

Multiple uses

CountermeasureOnce-only limits usage

Use after expiration

CountermeasureAuto-invalidated by Shopify

Converting more than balance

CountermeasureAlways check balance before conversion

Brute Force Prevention

Code format: 70934-AB12CD-500

Item	Content
Characters used	A-Z, 0-9 (36 types)
Digits	6 digits
Combinations	36^6 = ~2.1 billion patterns

Characters used

ContentA-Z, 0-9 (36 types)

Digits

Content6 digits

Combinations

Content36^6 = ~2.1 billion patterns

Brute force difficulty:

Even at 100 attempts/second, testing all patterns takes ~240 days
Plus rate limit of 60/minute

Additional measures: Temporary account lock on consecutive failures, detect abnormal patterns and alert

Conversion Rate and Limits

Points to Amount Conversion Rate

Base rate: 1 point = 1 yen

Points	Coupon Amount
100pt	100 yen off coupon
500pt	500 yen off coupon
1000pt	1000 yen off coupon

100pt

Coupon Amount100 yen off coupon

500pt

Coupon Amount500 yen off coupon

1000pt

Coupon Amount1000 yen off coupon

Future extensibility:

Campaign: 1pt = 1.5 yen
Member rank: Gold = 1pt = 1.2 yen
Design to be configurable

Conversion Limits

Limit	Value	Reason
Minimum conversion unit	100pt	Prevent small coupon proliferation
Maximum per conversion	10,000pt	Manual review for high amounts
Daily limit	30,000pt	Limit damage from fraud
Conversion increment	100pt steps	Avoid fraction handling complexity

Minimum conversion unit

Value100pt

ReasonPrevent small coupon proliferation

Maximum per conversion

Value10,000pt

ReasonManual review for high amounts

Daily limit

Value30,000pt

ReasonLimit damage from fraud

Conversion increment

Value100pt steps

ReasonAvoid fraction handling complexity

Customer Display

Coupon Information Display Items

Item	Coupon 1	Coupon 2
Code	70934-AB12CD-500	70934-XY34ZW-1000
Amount	500 yen off	1,000 yen off
Expiration	January 15, 2025	December 31, 2024
Status	Unused [Copy Code]	Used (10/20/2024)

Code

Coupon 170934-AB12CD-500

Coupon 270934-XY34ZW-1000

Amount

Coupon 1500 yen off

Coupon 21,000 yen off

Expiration

Coupon 1January 15, 2025

Coupon 2December 31, 2024

Status

Coupon 1Unused [Copy Code]

Coupon 2Used (10/20/2024)

Usage Instructions

Coupon Usage Guide

Add items to cart

Add products you want to purchase to cart

Proceed to checkout

Go to checkout screen

Find coupon code field

Look for coupon input field on checkout screen

Enter or paste code

Example: 70934-AB12CD-500

Click 'Apply'

Apply the coupon

Confirm discount applied

Subtotal: 5,000 yen → Coupon: -500 yen → Total: 4,500 yen

Benefits of This Design

Security

Minimize fraud risk
Limit damage even if issues occur
Traceable design for easy problem identification

Customer Experience

Clear, easy-to-understand amounts
Copy function reduces input effort
Sufficient validity period for stress-free use