Implement in working flutter application play sound from app or web

Hello, I have working flutter project. Backend is firebase. I need update a bit app, i need play mp3 sounds from inside my application. But all posts is in backend. So maybe in backend i need write just music file name, or smth like this. Hope you can help. Please check details, where i need add sound and how looks backend. Please write saparas job, it's mean you read this description. Please add real price. My budget is 20 USD. If you can do this, i have another small tasks for your. Regards.