code: public static function generateChecksum2(int $orderId, string $sharedKey, int $currency): string
      {
          return strtolower(md5($orderId.'+'.$sharedKey.'+'.$currency));
      }
docs: Dandomain has a bug in their payment implementation where they don't
  include amount in checksum on their complete/success page.
  That is why we have a second method for computing that checksum.
  
  @param int    $orderId
  @param string $sharedKey
  @param int    $currency
  
  @return string