Backend Web admin development

A app for electricians by an electric company. Electrician scan qr code on their mobile app and get credited bonus amount. Like 5 10 25 50 100 etc. The credits are reflected in their wallet. They can withdrawal to their paytm wallet(Less transaction fees ) or place a bank transfer request subject to minimum requirements. Also electricians can participate in a scheme and win exciting gifts like mobiles , bikes , cars etc. We need a robust backend (pref firebase bd ) and webadmin and api to develop mobile apps(Dart/Flutter) for the same. More admin details are attached. Candidate should work with my developers and be connected to collaborations tools. Candidate should be able to understand and solve queries. Candidate should be quick and fast to respond. Plz mention skills you will use for this development. (Server/db/programming lang/framework/libraries) and why ? Fit candidate can work longtime or project to project.