The Checkin app requires a phone with Android version 5.0 or newer. This means that most newer Android phones can run the app.
When you use the Checkin app on your Android phone, scanning is done using the built-in camera. There may be differences in the phones' ability to scan, simply because some cameras are better and faster at focusing than others. Additionally, the right amount of light is crucial. Therefore, make sure to avoid strong direct sunlight as well as poor lighting.