Mobile App Developer Required

I need a developer/team who can work on a mobile app with the following tech stack:

Front End

iOS: Swift
Android: Kotlin
Web: HTML, Bootstrap

Back End
PHP

Database
MYSQL

The mobile app is currently live with active nearly 3000 users this is a beauty marketplace app that allows customers to find local last minute appointments.

Functionality that needs working on:

- Wallet feature for both customer and business app needs improving, currently if a customer is refunded it goes straight to their bank rather than sitting as credit within their wallet with the option to use for later purchases or to withdraw.
- Businesses need the ability to have a calendar to set their availability (should sync with google/outlook calendars)
- Rescheduling appointments, the functionality there at the moment is not user friendly, this needs tying into the calendar feature so that if a client needs to reschedule they can chose a available time from the beauticians calendar.
- Special offer feature needs updating so that it works more like groupon special offers. (I can provide additional clarification on this)

If you feel you can help with the above please send me a quote and timeframe.