# Check discount code validity

Validates a discount code for a specific customer before checkout.

When to use this:
- During checkout when customer enters a loyalty discount code
- Before applying discount to verify it belongs to the customer
- To check discount status and expiry
- To retrieve discount details (type, value, restrictions)

Request body:
- customerId: Shopify customer ID (required)
- discountCode: The discount code to validate (required, case-insensitive)

What this endpoint checks:
- Discount code exists in the system
- Code belongs to the specified customer
- Code status is "UNUSED" or "ACTIVE"
- Code has not expired
- Code is valid for current context

Response includes:
- Discount type (PERCENTAGE, FIXED_AMOUNT, FREE_SHIPPING, FREE_PRODUCT)
- Discount value (percentage or fixed amount)
- Expiry date
- Usage restrictions (minimum purchase, specific products, etc.)
- Points that were redeemed for this code
- Shopify discount code ID for reference

Discount statuses:
- UNUSED: Code has not been used yet (valid)
- ACTIVE: Code is being used in an active subscription (valid for renewals)
- USED: Code has already been redeemed (invalid)
- EXPIRED: Code has passed expiry date (invalid)

Integration pattern:
1. Customer enters loyalty code at checkout
2. Call this endpoint to validate the code
3. If 200 response, apply discount in checkout
4. After order is placed, call update-discount to mark as USED
5. Handle 400/404 by showing error message to customer

Common scenarios:
- Valid code: 200 with full discount details
- Wrong customer: 404 (code exists but for different customer)
- Already used: 400 with "Discount already used" message
- Expired: 400 with expiry information
- Invalid code: 404 (code doesn't exist)

Endpoint: PUT /api/external/check-discount

## Request fields (application/json):

  - `customerId` (integer, required)
    Shopify customer ID (numeric). Identifies which customer is attempting to use the discount code.
Used to verify the discount code belongs to this customer.
Example: 67890
    Example: 67890

  - `discountCode` (string, required)
    The discount code to validate. Case-insensitive.
This is the code the customer enters at checkout.
System will check if:
- Code exists in loyalty system
- Code belongs to this customer
- Code status is UNUSED or ACTIVE
- Code has not expired
Examples: "LOYALTY15OFF", "VIP20", "WELCOME10"
    Example: "LOYALTY15OFF"

## Response 200 fields (application/json):

  - `id` (integer)

  - `shop` (string, required)

  - `customerId` (integer, required)

  - `description` (string)

  - `pointTransactionId` (integer)

  - `pointRedeemRuleId` (integer)

  - `discountCode` (string, required)

  - `usedAt` (string)

  - `orderId` (integer)

  - `orderName` (string)

  - `status` (string, required)
    Enum: "USED", "UNUSED", "REFUNDED", "EXPIRED", "SUBSCRIPTION_ACTIVE"

  - `createAt` (string, required)

  - `expireDate` (string)

  - `variantId` (integer)

  - `discountCodeId` (string)

  - `productData` (string)

  - `usageCount` (integer)

  - `amount` (number)

  - `rewardType` (string)
    Enum: "STORE_CREDIT", "DISCOUNT_CODE", "POINTS"

  - `lastExpiryReminderSentDate` (string)