How to send a message in the Slack channel using Flutter?

Finally got the answer, and wants to share :)

Here is the slack API URL to create a new app:-

https://api.slack.com/apps

After creating a new app, activate the Incoming Webhooks feature:-

Grab the webhook URL for your workspace, and make a request via this Flutter function:-

import 'dart:convert';
import 'package:http/http.dart' as http;

sendSlackMessage(String messageText) {
  //Slack's Webhook URL
  var url = 'https://hooks.slack.com/services/TA******JS/B0**********SZ/Kk*******************1D';

  //Makes request headers
  Map<String, String> requestHeader = {
    'Content-type': 'application/json',
  };

  var request = {
    'text': messageText,
  };

  var result = http
      .post(url, body: json.encode(request), headers: requestHeader)
      .then((response) {
    print(response.body);
  });
  print(result);
}