Not sure if it will work for you.
In my App - Order online
For the App client i use push notifocations to inform the status.. (plus the user can refresh to know the status of he/she order)
To recive the order in the restaurant i just (automatic) refresh the App (in the kitchen) each 10 sec.
here an old video of a demo:
Our POS system first version around March 2014! EDIT: and here the web platform to add/edit/delete dishes, get reports... uSAAS-POS Edit: and the takeaways app: Edit: We added a simple Order+Delivery to our POS: