Watch for changes to calendar, when to make request - react-native

Question

When watching for changes to a collection of events on a given calendar, how often do I need to make a watch request?
Where would I put my code to make a watch request? Does it only need to be done once?
My code below gets an access token and makes a post to create a watch channel, however I'm not sure where to host the code or how often I need to run it:
let { google } = require("googleapis");
let functions = require("firebase-functions");
let privatekey = require("./config.json");
let axios = require("axios");
let jwt = new google.auth.JWT(
privatekey.client_email,
null,
privatekey.private_key,
["https://www.googleapis.com/auth/calendar"]
);
const token = await jwt.authorize();
let headers = {
"Access-Control-Allow-Origin": "*",
"Content-Type": "application/json;charset=UTF-8",
Authorization: token.token_type + " " + token.access_token
};
let data = {
id: randomId,
type: "web_hook",
address: "https://rguc-calendars.firebaseapp.com/notifications",
params: {
ttl: 3600
}
};
axios
.post(
"https://www.googleapis.com/calendar/v3/calendars/thirdyear#rguc.co.uk/events/watch",
data,
{ headers }
)
.then(function(response) {
// success
})
.catch(function(error) {
// error
});

Answer 1

push notifications
The Google Calendar API provides push notifications that let you watch
for changes to resources. You can use this feature to improve the
performance of your application. It allows you to eliminate the extra
network and compute costs involved with polling resources to determine
if they have changed. Whenever a watched resource changes, the Google
Calendar API notifies your application.
Register the domain of your receiving URL.
For example, if you plan to use https://example.com/notifications as your receiving URL, you need to register https://example.com.
Set up your receiving URL, or "Webhook" callback receiver.
This is an HTTPS server that handles the API notification messages that are triggered when a resource changes.
Set up a notification channel for each resource endpoint you want to watch.
A channel specifies routing information for notification messages. As part of the channel setup, you identify the specific URL where you want to receive notifications. Whenever a channel's resource changes, the Google Calendar API sends a notification message as a POST request to that URL.
Once you have set up the watch google will notify you when ever there is a change you wont have to call it again.