make a flutter chat app

I need a fully-featured Flutter Chat app that is compatible with both iOS and Android. This chat application should offer users all the features they look for in a messaging app, and that includes end-to-end encryption and group chat functionality. This app should be developed with the latest technologies and tools to ensure that it is fast, secure, and efficient. The project doesn't have a time limit, so it would be great if the development could be done in the most efficient and cost-effective manner possible.