Hi there
I have worked with bluetooth beacon in the background and it has some difficulties but it's completely doable.
I am an Android and iOS expert with a deep experience in building apps in Java and Swift, also, I have a good experience in building apps using hybrid languages like React Native and Flutter and Kotlin, by hybrid languages you can have both Android and iOS versions using one code.
Also, I can build the backend using Node.js and MongoDB or Google Firebase.
Please contact me via chat to talk more about the project details.
Also, I will support the app for 6 months for any bugs.
Thanks
Best regards
Nick