I can't enter chords at all. I type them in and hit "enter" on my keyboard (Apple "magic" keyboard - short version), and it either leaves the measure blank or if its the default "C" chord it changes immediately back to C. Please help a newbie!

Is the latest build installed?

It's build 309 and was released 15 October and is available for download at the below site.

https://www.pgmusic.com/support_macintoshupdates.htm

1. Does it do this plugged in as well as wireless? Weak wireless connection perhaps?
2. When is the last time you recharged the battery? Weak battery?
3. Run a keyboard test if Apple includes one.
4. Keyboard language changed?
5. Running a macro by accident?

If you load any demo song, do you actually SEE any chords on the Chord Sheet? What about notation in the Notation Window?

Are you able to change the name of the song, indicating that the keyboard works for other tasks?
Also, perhaps try entering a search string in the StylePicker. Does that work?