How can I use Communications module to work with webservices in Garmin WatchFace App.

When you have a watch face, the way you do comm is by way of a background process.  The watch face has a background process that does the comm, say every 10 minutes, which returns the data to the watch face.

Here's a blog post I did a few years back with the basics of doing a background service:

https://developer.garmin.com/index.php/blog/post/guest-post-creating-a-connect-iq-background-service

Okay. I will try your solution.

Thank you for the quick reply. Will you please clear my doubt related to the ClientId, please.
Thanks

I'm not sure what you mean with client id.  I'n many of mine I use an APIKEY, which I get from Application.properties in the background - the user sets it with app settings.

Okay,
btw is the below code snippet will be enough for doing the web-service action?  

        // Make the request to display the OAuth page in GCM
        Communications.registerForOAuthMessages(method(:onOAuthComplete));
        Communications.makeOAuthRequest(Constants.PROVIDER_URL, 
        {"redirectUrl" => Constants.REDIRECT_URL}, 
        Constants.REDIRECT_URL, 
        Communications.OAUTH_RESULT_TYPE_URL, 
        {"token" => "token", "errorMessage" => "errorMessage"});
        
        // Callback for OAuth completion
        function onOAuthComplete(data) {
        // If OK, store the token. Otherwise show the error.
        if ((data.responseCode == 200) && (data.data != null)) {
            var token = data.data["token"];
            if (token != null) {
                Application.getApp().setProperty(Properties.AUTHENTICATION_TOKEN, token);
                WatchUi.popView(WatchUi.SLIDE_IMMEDIATE);
            }
        } else if (data.data != null) {
            var message = "Unable to get token:\n" + data.data["errorMessage"];
            WatchUi.switchToView(new ErrorView(message), null, WatchUi.SLIDE_IMMEDIATE);
        } else {
            var message = "Unable to get token:\nUnknown error";
            WatchUi.switchToView(new ErrorView(message), null, WatchUi.SLIDE_IMMEDIATE);
        }

        Communications.registerForOAuthMessages(null);
    }

for ClientId, please check the below snippet and URL from which I am taking reference for integration:

reference link: https://developer.garmin.com/downloads/connect-iq/monkey-c/doc/Toybox/Communications.html#makeOAuthRequest-instance_method

// wrap the OAuth request in a function
function getOAuthToken() {
   status = "Look at OAuth screen\n";
   Ui.requestUpdate();

   // set the makeOAuthRequest parameters
   var params = {
       "scope" => Comm.encodeURL(https://www.serviceurl.com/),
       "redirect_uri" => "http://localhost",
       "response_type" => "code",
       "client_id" => "$.CLIENT_ID"
   };

   // makeOAuthRequest triggers login prompt on mobile device
   Comm.makeOAuthRequest(
       "https://requesturl.com",
       params,
       "http://resulturl.com",
       Comm.OAUTH_RESULT_TYPE_URL,
       {"responseCode" => "OAUTH_CODE", "responseError" => "OAUTH_ERROR"}
   );
}

You should be able to do this, but all the comm has to be done in the background process.  You might want to look into onAppInstall() to get things started.

Thanks for the reply, Jim. I will try implementing now. Will ask for further queries to you.
Thanks Again.