The Push Messaging server responds with HTTP status code 500
(internal server error) if the app that calls the pushMessaging API
is not found in the Chrome Web Store. This ownership check
is designed to prevent people from sending messages to your app
without your permission. Commonly this error occurs during
development if you run a version of your app without the correct
key attribute in its manifest file.
To fix this problem, simply install your app from
the Chrome Web Store and copy the key
field from manifest.json in the installed app to manifest.json in
the version of the app that you are developing
(see Testing in the cloud for
detailed instructions). Note that you need to remove the key
field from manifest.json before you upload the app to the Chrome Web Store again.