Thorough testing is an essential part of designing and building any great app.
Test on an actual CarPlay-compatible display, preferably in a car. Make sure your app is easy to see and navigate from different driver positions, under different weather conditions, and at different times of day.
Test with poor network conditions such as while driving through a tunnel and in an area without cellular reception. Make sure your app handles connection losses and a lack of data gracefully and nonintrusively.
Test installation and setup. Install your app on a physical iPhone. Pay close attention to any sign-in requirements and privacy dialogs, and make sure your app appears as expected in CarPlay.