Hello, I'm doing this post because I couldn't find this in the docs of Zeplin, so you avoid a headache :)
Your UX/UI designer exported all the screens and components into Zeplin and you are developing in RN. In the web version you get to the component code snippet part and you'll see a XML snippet and no RN version.
Add React Native extension to Zeplin Web
When you click there, and if your screen has the same height of mine, you'll have the same problem I had.
The header of the modal gets cropped, so you can't go to the extensions page. Just click F11 to enable Fullscreen and see the header:
Then click Extensions and enable RN: