You are opening your application and an "Application Error" message is displayed.
"Application Error" or similar is always caused by your own application code. Routing errors will normally only surface themselves within the logs of your application.
To track this kind of issue down you should look at your logs:
$ heroku logs --tail --app your_app_name
If you can't see the source of the error straight away, try restarting your app from another terminal window or via the Heroku Dashboard:
$ heroku restart
There are some errors which only occur when the app is rebooting so you will need to restart the app to see these log messages appear.
For most apps, we also recommend enabling one of the free logging addons from https://elements.heroku.com/addons#logging to make sure that your historical log data is being saved. Many of these have searchable web interfaces which can be helpful in tracking issues over time.
If you find an error message that you don't understand, try checking out the following resources:
- Heroku Error Codes (H12, R14, R15, H10, H14 etc.) - https://devcenter.heroku.com/articles/error-codes
- Postgres Errors - https://devcenter.heroku.com/articles/postgres-logs-errors
- Language/App errors - Stack Overflow http://stackoverflow.com/