Make sure you’re running a packager server or
have include a .jsbundle file in your application
bundle.
If you are getting this error in React Native App. you can follow the following steps to fix
Video Tutorial
Step 1:
Open the package.json file and add the following line
"build:ios": "react-native bundle --entry-file='index.js' --bundle-output='./ios/main.jsbundle' --dev=false --platform='ios'"
Now your file looks like this following screenshot