[Flutter] Bank Alfalah Payment Gateway in Flutter: Exception Thrown Despite Success Response

I'm integrating the Bank Alfalah payment gateway in my Flutter app. I have the following code for initiating a payment request. Even when I receive a "success": true response, I'm still encountering an exception. I've tried generating the request hash using HMAC SHA-256 encryption, but my generated hash doesn't match the static hash key provided, and I'm not sure if this is causing the issue.

int bankOrderId = Random().nextInt(1786612);
var transactionReference = bankOrderId.toString();

var dataString = "HS_ChannelId=$channelId&HS_IsRedirectionRequest=0"
"&HS_MerchantId=$merchantId&HS_StoreId=$storeId"
"&HS_ReturnURL=$returnUrl&HS_MerchantUsername=$username"
"&HS_MerchantPassword=$password&HS_TransactionReferenceNumber=$transactionReference";

var encryptedRequestHash = _encryptData(dataString);

try {
var response = await http.post(
Uri.parse(url),
body: {
// "HS_ChannelId": channelId,
// "HS_IsRedirectionRequest": "0",
// "HS_MerchantId": merchantId,
// "HS_StoreId": storeId,
// "HS_ReturnURL": returnUrl,
// "HS_MerchantHash":
// "My MerchantHash",
// "HS_MerchantUsername": username,
// "HS_MerchantPassword": password,
// "HS_TransactionReferenceNumber": transactionReference,
// "HS_RequestHash": encryptedRequestHash,
"HS_ChannelId": "My channel Id",
"HS_MerchantId": "My Merchant Id",
"HS_StoreId": "My Store Id",
"HS_ReturnURL": "xyz",
"HS_MerchantHash": "My HS_MerchantHash",
"HS_MerchantUsername": "my username",
"HS_MerchantPassword": "my pass",
"HS_TransactionReferenceNumber": "12345", "HS_RequestHash":"vU9+EdDzpTIjhxJMT4v/EfAycy/Eo6+U4wuCo0lMaf2gOz95IXHe6LdwxcVvQh7VEp2cqz32OPtJIPQlebnlVCpmCKXMOiVExLn87vq0Fd31Wm/VpyUbogHMrLoYQv23gMOpvethLE2CA39VLGDeYI98VA8wKM+ZVmLZv1QqZ3FCfkgM+ciIh8cygpa4A0zKQD7hj8x+xlSKsRY2dPrSFdPDdkUPw37ST5v7Mj7UMSvljdiBQTuY0ri9goWowpfclgpBdu1RFbOSJSr/AshY/NYCOgTC638YS1g=="
},
);

// debugPrint the raw response body
debugPrint("Response Body: ${response.body}");

// Decode the response body as JSON
var jsonResponse;
try {
jsonResponse = json.decode(response.body);
debugPrint("Decoded JSON Response: $jsonResponse");
//debugPrint("Type of success: ${jsonResponse["success"]?.runtimeType}");
} catch (e) {
debugPrint("Error decoding JSON: $e");
throw Exception("Failed to decode JSON response: $e");
}

// Ensure jsonResponse is a Map and contains 'success'

// debugPrint type of 'success' and other fields
// debugPrint("Type of success: ${jsonResponse['success']?.runtimeType}");
// debugPrint(
// "Type of AuthToken: ${jsonResponse['AuthToken']?.runtimeType}");
// debugPrint(
// "Type of 'ErrorMessage': ${jsonResponse['ErrorMessage']?.runtimeType}");

if (response.statusCode == 200) {
// debugPrint("Type of AuthToken: ${jsonResponse['AuthToken']}");
// return {
// "authToken": jsonResponse["AuthToken"],
// };
} else {
// Log the error message returned by the API
// debugPrint("Error Message: ${jsonResponse['ErrorMessage']}");
throw Exception(
"Payment initiation failed: ${jsonResponse['ErrorMessage']}");
}
} catch (error) {
// debugPrint("Error initiating payment: $error");
throw Exception("Error initiating payment: $error");
}
throw Exception();
}

// Encrypt data using HMAC SHA-256 with base64 encoding
static dynamic _encryptData(var data) {
var key = utf8.encode(key1); // Use key1 as the HMAC key
var hmac = Hmac(sha256, key); // HMAC with SHA-256
var digest = hmac.convert(utf8.encode(data)); // Convert data to hash
return base64.encode(digest.bytes); // Encode hash in base64
}```

Thanks for any guidance or insight!

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