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Bolt Help / Core Products / Checkout / Custom Cart Checkout / Bolt Checkout Direct API Integration Guide / How to Apply Discounts
How to call the Merchant Callback API and verify discount codes submitted by a shopper.
Use the Merchant Callback API to handle shopper’s coupons, promo codes, or other discounts added to their carts.
How to Use the Discounts API
The discounts.code.apply endpoint is called when a shopper enters a discount code; it is recalled whenever the cart or chosen shipping option is updated.
- Implement the discount Merchant Callback API on your server.
- Respond to Bolt’s
discount.code.applyPOST request via your Merchant Callback API. - Verify the authenticity of the request by confirming that it originated from Bolt.
PHP Example
<?php
require(dirname(__FILE__) . '/init_example.php');
$hmacHeader = @$_SERVER['HTTP_X_BOLT_HMAC_SHA256'];
$signatureVerifier = new \BoltPay\SignatureVerifier(
\BoltPay\Bolt::$signingSecret
);
$requestJson = file_get_contents('php://input');
if (!$signatureVerifier->verifySignature($requestJson, $hmacHeader)) {
throw new Exception("Failed HMAC Authentication");
}
$requestData = json_decode($requestJson);
header('Content-Type: application/json');
if (@$requestData->type == 'discounts.code.apply') {
$couponCode = @$requestData->discount_code;
if ($couponCode == \BoltPay\Example\Data::VALID_COUPON) {
$response = [
'status' => 'success',
'discount_code' => $couponCode,
'discount_amount' => 1000,
'description' => 'Discount (BOLT-DEMO)',
'discount_type' => 'fixed_amount'
];
http_response_code(200);
} else {
$error = new Exception("Coupon code is invalid");
$response = [
'status' => 'failure',
'error' => [
'code' => $error->getCode(),
'message' => $error->getMessage(),
],
];
http_response_code($error->getCode());
}
}
echo json_encode($response);
WARNING
Applying a discount amount that is more than the total order amount will result in an error. It is recommended you calculate a max allowable discount amount using the formula line item totals + tax + shipping = max allowable discount.
How to Test
To ensure this step is complete, precisely follow the instructions below.
- Open Bolt Checkout and enter a discount code.
- Bolt should hit your discount merchant API.
- If the discount is valid, check that Bolt applies the correct discount amount to the cart.
- Repeat the test with an invalid discount too ensure that Bolt:
- Does not apply any discount amount.
- Correctly alerts the user.
Handling Errors
To respond with specific errors in merchant api responses visit the error codes reference article.