Hi guys, 

I needed to send a push notification with the Title and the message as the screenshot below shows:

By looking at the rest api documentation looks like that in order to set the title we should send the headings parameter:

So I went into OneSignal API where the call to that rest API is made and added a new parameter called headings of the same type as messages. Also exposed that parameter on every action calling PostNotification.

Now I can successfully send push notifications with title and message through one signal plugin.

Are you planning on releasing this feature on official version ?