Signature Validation Helper

curl --location --request POST 'https://subscription.be.pkbsvc.com/webhook/onerway/callback' \
--header 'Content-Type: application/json' \
--data-raw '// ---------------------- Instructions ----------------------
// 1. Configure your credentials in the environment variables:
//    - merchantNo: Your merchant account number
//    - secret: Your secret key
//    - appId: Your application identifier
//
// 2. Replace the template below with your actual request payload
//
// 3. Send the request and view the generated signature in the console
//    (The signature will be displayed in console)
// -----------------------------------------------------------

{
    "billingInformation": "{\"country\":\"CN\",\"email\":\"{{email}}\"}",
    "merchantCustId": "558361",
    "merchantNo": "{{merchantNo}}",
    "merchantTxnId": "VIP202403301711805804608609616",
    "orderAmount": "0.03",
    "orderCurrency": "USD",
    "paymentMode": "WEB",
    "productType": "CARD",
    "shippingInformation": "{\"country\":\"CN\",\"email\":\"{{email}}\"}",
    "sign": "62fc1e9d5c6d4e1b2b9a58a34b349d99bac6bde1505dd20b5949e80d97b417f0",
    "subProductType": "TOKEN",
    "txnOrderMsg": "{\"accept\":\"application/json, text/plain, */*\",\"appId\":\"{{appId}}\",\"colorDepth\":\"30\",\"contentLength\":\"300\",\"javaEnabled\":\"false\",\"language\":\"zh\",\"notifyUrl\":\"https://api-dev-www.shakker.ai/pay/callback\",\"products\":\"[{\\\"currency\\\":\\\"USD\\\",\\\"name\\\":\\\"基础版VIP 12个月\\\",\\\"num\\\":\\\"1\\\",\\\"price\\\":\\\"0.03\\\"}]\",\"returnUrl\":\"https://api-dev-www.shakker.ai/training\",\"screenHeight\":\"1117\",\"screenWidth\":\"1728\",\"timeZoneOffset\":\"-480\",\"transactionIp\":\"transactionIp\",\"userAgent\":\"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/123.0.0.0 Safari/537.36\"}",
    "txnType": "SALE"
}'