I have a project developed in IONIC 2 and I generated the version for IOS but I have a problem with OneSignal. I have already tried to reinstall the plugin by ionic but problem still continues.
Try installing CocoaPods and then remove and re-add the onesignal
plugin. CocoaPods makes it easy to implement libs in xcode.
sudo gem install cocoapods
pod repo update
If even after the above procedure the error continues, try to open the file .xcworkspace
instead of .xcodeproj