String stringToHash = amount=100&callbackUrl=https://checkout.seerbit.com/?m=EQREZEhyRn&country=NG¤cy=NGN&email=kolawole@gmail.com&paymentReference=5fgj77treo&productDescription=RiceandBeans&productId=Foods&publicKey=EQREZEhyR
String hashString = stringToHash + privateKey;
Hash = Sha256(hashString);
public static String Sha256(String rawKey) throws ProcessingException {try {MessageDigest md = MessageDigest.getInstance("SHA-256");byte[] encrypted = md.digest(rawKey.getBytes());return new String(Hex.encodeHex(encrypted));} catch (NoSuchAlgorithmException ex) {String errorMessage = "Unable to hash this string";throw new ProcessingException(errorMessage);}}