This one is a common mistake and one that I have made myself when I started working in React Native. I use to focus most of my development time on iOS without testing them on Android. While React Native is a cross platform tool, there are a lot of features that behave differently or are completely lacking on Android in comparison to iOS.
Even if you choose to focus on one platform at first, it is recommended that you always check both, especially if you are installing a lot of third-party libraries. React Native is constantly changing and the libraries you are using probably cannot keep up with all the breaking changes being introduced. If you want to avoid making bad decisions and identifying potential road blocks early, make sure you always check both platforms.
Even better, focus on Android and check iOS. This is because Android is the platform most likely to make you run into issues.
