https://pub.dartlang.org/packages/firebase_remote_config

import 'package:firebase_remote_config/firebase_remote_config.dart';

void initState() {
  super.initState();

  RemoteConfig.instance.then((remoteConfig){
    remoteConfig.setConfigSettings(RemoteConfigSettings(debugMode: true));

    try {
      remoteConfig.fetch(expiration: const Duration(minutes: 1));
      remoteConfig.activateFetched();
    } catch(error) {
      print("Remote Config: $error");
    }

    final mensagem = remoteConfig.getString("mensagem");

    print('Mensagem: $mensagem');
  });
}