Unable unpackage the message from UXP to DLL

Photoshop UXP Plugin API
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1

Hi, thanks for watching
I follow the sample code of Listener in the folder of automation.
I am trying to receive a message from UXP to DLL.
I can enter the callback function*: MyUXPNotifier based on the provided sample code.
However, the message I received could not be able to unpackage by using the code provided.
I am wondering if the message structure that I sent is correct.
Sincerly thanks again, for any help. :smiley:

void MyUXPNotifier(PIActionDescriptor descriptor)
{
	Logger logFile("ListenerUXP");
	LogPrint(L"ListenerUXP");

	if (descriptor)
	{
		Boolean hasKey = 0;
		**OSErr error = sPSActionDescriptor->HasKey(descriptor, keyMessage, &hasKey);**
		if (error == kSPNoError && hasKey)
...

async function SendMsgBack2DLL()
{
    **let messageContent = {Msge: "ok" };**
    try
    {
        // 1@param :Give the plugin name from addon name in manifest.json.
        const res = app.messaging.sendSDKPluginMessage("Listener", messageContent);
        console.log(`Send Message result ${res.message.toString()}`);
        messageDialog(`Send Message result ${res.message.toString()}`);
    }
    catch (err)
    {
        console.log(`Message command failed ${err}`);
        messageDialog(`Message command failed ${err}`);
    }
}
2

Is there any document of the API: sendSDKPluginMessage?
How do I know that Photoshop packages the messages with keyMessage or other keys?
Thanks for any help :blush: