Hi! My name is Guillermo, I'm a Director at Aurora Studio, a Development Studio based in the United States and I would like to help you with your project!
It seems like you are looking to develop a Mobile APP, I recommend working with React for the frontend, that way you can reach both Android and iOS Devices. As well as C# for the API Server
If possible, could you tell me a bit more about your requirements and specifications? As well as the features you are looking to develop?
I'm in the chat if you need me. If you have any questions, feel free to ask!