Steps to success:

1. Make sure you have enabled iCloud in the app id
2. Make sure you have deleted and re-created the development and distribution profiles (NOTE: make sure the development one is done in particular as this is most likely the one used while your testing)
3. Ensure the following keys are present in your [target].entitlements file (customise the com.mycompany… as needed)

• $(TeamIdentifierPrefix)com.mycompany.myapplication
• $(AppIdentifierPrefix)com.mycompany.myapplication