Implement Socket.IO client on your platform and listen to this URL:
Production - https://api.sensepass.com?id=id_<Device_Id>
Sandbox - https://api.sandbox.sensepass.com?id=id_<Device_Id>
Listen to "message" event to get notifcations about the transaction for a specific device.
Read here about Socket.IO: https://socket.io/docs/