getCheckValue function
Implementation
String getCheckValue({
required String merchantKey,
required String merchantToken,
required String invoiceId,
required String amount,
required String currencyCode
}) {
String hash1 = sha512.convert(utf8.encode(merchantToken)).toString().toUpperCase();
String hash2 = sha512.convert(utf8.encode("$merchantKey|$invoiceId|$amount|$currencyCode|$hash1")).toString().toUpperCase();
return hash2;
}