public function _callbackValidCurrency($sCode)
    {
        $oFormValidation = Factory::service('FormValidation');
        $oFormValidation->set_message('_callbackValidCurrency', 'Invalid currency.');

        $oCurrency = Factory::service('Currency', 'nails/module-currency');
        $aEnabled  = $oCurrency->getAllEnabled();

        foreach ($aEnabled as $oCurrency) {
            if ($oCurrency->code === $sCode) {
                return true;
            }
        }

        return false;
    }