You can simply encode the JSON and see the list of keys which are receiving in the Push payload. Once you print the JSON string,you can parse it accordingly on the client side.
To encode the JSON string, simply use the below code and let us know if you need any other help from our side.
local JSON = require("App42-Lua-API.JSON")
Also, I would request you to put a comment on same thread instead of creating a new question. It will help us to serve better.