> ## Documentation Index
> Fetch the complete documentation index at: https://developer.transactbridge.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Integration at Customer Checkout

The coupon system allows the partner the flexibility to use their coupon store and let their customer apply coupon codes at the Transact Bridge checkout page.

Since the coupon validation is performed entirely by the merchant, partners can implement any custom business logic, such as:

* Percentage-based or fixed amount discounts.
* Coupons with start and expiry dates.
* One-time or limited-use coupons.
* Customer-specific or segment-specific offers.
* Product or subscription plan-specific discounts.
* Minimum purchase amount requirements.
* Referral, promotional, loyalty, or campaign-based coupons.

## Customer Coupon Verification Flow

```mermaid theme={null}
sequenceDiagram

participant Customer
participant Checkout as TB Checkout
participant Merchant

Customer->>Checkout: Enter Coupon Code
Checkout->>Merchant: Coupon Verify API
Merchant->>Merchant: Validate Coupon
Merchant-->>Checkout: Valid / Invalid Response

alt Coupon Valid
Checkout->>Customer: Discount Applied
else Coupon Invalid
Checkout->>Customer: Invalid Coupon Message
end
```

***

## Steps for Integration

When a customer enters a coupon code on the hosted checkout page:

1. Transact Bridge calls the configured **<a href="https://docs.transactbridge.com/#e794037e-c3be-4250-a54a-470852f07a37">Coupon Verify API</a>**.
2. The merchant validates the coupon code.
3. The merchant returns the discount details.
4. If the coupon is valid, the discount is applied to the checkout.
5. If the coupon is invalid, an appropriate error message is displayed to the customer.

The expected response from the merchant is described in the **<a href="https://docs.transactbridge.com/#e794037e-c3be-4250-a54a-470852f07a37">Coupon Verify API Documentation</a>**.

***

## Configuring the Coupon Verify API

To configure the Coupon Verify API endpoint:

1. Log in to the **Transact Bridge Dashboard**.
2. Navigate to **Account Settings**.
3. Configure the **Coupon Verify Callback URL** under callback urls.
4. Save the configuration.

Once configured, Transact Bridge will invoke this endpoint whenever a customer attempts to apply a coupon on the hosted checkout.