Monthly contract addition in the existing app

I am looking to hire somebody to add a new monthly contract onto an existing app. This app is currently on the Android and ios platform. I am looking for somebody to take on this project as a one-time payment instead of a monthly subscription. This monthly contract will require some new features to be added to the app, so I need somebody who has experience in developing for php, nodejs, java, swift, mongodb. and integrating new features. Interested parties should have a portfolio of past projects as well as experience and knowledge in coding this feature. I am also open to considering proposals from potential candidates who can provide support and maintenance in the future.