How to prevent two users from using the same account in different smartphone?
You can check they IP, phone IMEI,etc and check with the account that was created.
I use login my app with sign in with google component.
I think it is safe way.
Do you can show me an example, please
Adding to @Chocoduba_BR ,
You can also use Device ID block.
You can sign up user with their device id and store device ID block to database and when user signin, check if device ID is same or not.
Device ID is unique for every device.