I'm using expo react native and I want to do something similar to whatsapp (check if contacts downloaded the app so I can give them some permissions, and if a contact doesn't have the app I can invite him).
The problem is that I don't know how to start. Where should I read the contacts? Should I return them to server-side or read them from phone ? What are key words or concept I should read about and follow to take the right path doing this ?