Follow instruction at Smartthingsto create and configure the SmartApp.
Follow the documentto subscribe the things event. An example at githubshows a sample code snippet of a working SmartApp – provides a HTTP GET API interface to list all the available things and the data.
Also, follow the Firebase document to setup the client device SDK and note down the client device token, and the firebase server key.
Write an event data handler to process the event and send downstream message by http POST. Sample code can be seen below.