Getting this error while building a react-native iOS app on xcode.
Started getting this error after npm install and rpm linking react-native-fs library. But
After React Native 0.60 this issue is often caused by a linked library mixed with the new 'auto-linking' feature. This fixes it for me
Unlink old library using
$ react-native unlink react-native-fs
Refresh Pods integration entirely using
$ pod deintegrate && pod install
Now reload your workspace and do a clean build.