QR Scanning Android App

We Need an Android app which can scan a QR code (and/or barcode) from a phone/tablet/paper. The code needs to be validated against a database (we can provide an API endpoint to our .net / sql server or provide direct access to our SQL Server if easier/faster). Some information (valid/ticket holder name etc) needs to be retrieved from the API/database and a record inserted into the database with the date and time of the scan (and possibly other indicators/flags). This is for scanning football tickets at a turnstile and validating Club Memberships / Season Tickets / Match Tickets. We have almost completed the website allowing customers to obtain/buy tickets/memberships and deliver them via Email or the club portal. We now need to be able to scan those tickets at the turnstile using a mobile app (Android only) to admit people quickly with a pop up on the app if the ticket is not valid / concession expired and / or other conditions. We are on a short(ish) timescale (one month or less would be good) and so speed of development IS a factor but so is cost as our client is a local community based club. As .net developers we don't work with Android and we don't have time to develop using Xamarin in C#. We will require commented source code and would prefer a C# Xamarin solution if possible but this is not essential as we will also require the app to be supported going forward should updates to the ticket system need to be made affecting the app functionality. This is an application for one local football team that we will be marketing to other clubs and so this app may need re-branding and supporting for many more customers going forward. Our client is looking for a low cost , effective solution and we as the developer of the web site are happy to market this "total solution" to other clubs across the UK so a potential revenue stream in the future is definitely something we are happy to work with the successful app developer on. We will be entering into a partnership agreement with our client to market their total solution to other small clubs with their help to reach the other clubs in return for us providing a lower cost solution overall. We require a developer who can work closely with our CEO (lead developer) to get this solution implemented securely and with a fast throughput. IOS is absolutely not needed as the EPOS systems we have put in place and all of the customer facing tech is Android based. We prefer UK based developers with excellent English language and communication skills and ideally based in the Midlands (we are based in Nottinghamshire). We understand this to be a relatively simple project in terms of functionality and we have a database schema and flow available. A non-disclosure agreement will need to be entered into and we expect the developer of the app to be compliant with GDPR and registered with the ICO. A successful deployment would also ideally allow to market other apps to our other website clients in the future in what we would hope would be a mutually beneficial long term relationship.