I'm having this exact problem.
Did you succeed in resolving it ? If so could you post a how-to please.
I do have the Rex Parse Initialize updated to the latest, installed and filled with ID, Key and URL but I only get "Login failed" message.
On Heroku, my https://[app name].herokuapp.com/ returns:
"Make sure to star the parse-server repo on GitHub!"
which leads me to believe it's setup properly.
https://[app name].herokuapp.com/parse returns:
which the tutorial indicates is the expected response.
All the events in my .capx are setup as indicated in the tutorial.
Any clue on what I might be missing ?