"No .xcodeproj file found" during iOS Cordova build

Cordova released cordova-ios@8.0.0 in late November, which changes the name of the build target to App instead of using the name specified in a project's config.xml. The latest version of cordova-ios is automatically pulled down if an older version isn't already installed as a project dependency. Using this new version will cause the build to fail in Appflow.
 
Ionic is working on a means to support this change without dropping support for older cordova-ios versions. In the meantime, you can work around this issue with the following steps:

1. Install an older version of cordova-ios as a project dependency (npm install -D cordova-ios@7.1.1)
2. Commit the changes to your package.json
3. Rebuild your project in Appflow

Pinning an older version will ensure that Appflow builds your iOS project without installing the new cordova-ios release.