try to add plugix iapios in cocos2dx-lua,there are some problems

[lpcdma]

The first time I tried to complete such a code, please understand.
I use the sandbox test account, I think the result should be a JSON string,but I can't get it.

void ProtocolIAP::onPayResult(PayResultCode ret, const char* msg)
{
_paying = false;
if (_listener)
{
_listener->onPayResult(ret, msg, _curInfo);
}
else
{
PluginUtilsIOS::outputLog("Pay result listener of %s is null!", this->getPluginName());
}

_curInfo.clear();
PluginUtilsIOS::outputLog("Pay result of %s is : %d(%s)", this->getPluginName(), (int) ret, msg);

}
in this code ret is 0 to complete the purchase,and the _listener is null,cannot Lua callback function

If I want to get the JSON string pay for results, and will be the string callback to Lua, how should I do? Please help, thank you！