I changed to CloudKit and changed the extension as well to ".md". I was able to add a calendar event once or twice, then the same issue came up again where it could not add event and asked me to email support. I've deleted the app and reinstalled a few times. Anything else I can try?
I'm looking into the event creation problem. Restarting should usually help at least temporarily.
Any plans to implement Dropbox sync? iCloud or CloudKit is a no go for me.
Dropbox is an option already, but it's not as stable and has problems.