Why did my AirPort Express stop working?
The latest firmware won't work with Porthole. You can downgrade it.
Make sure to check your spam folder (for all email addresses that you use) and search your mailbox for “FastSpring” and the name of the app.
If that didn’t turn up your license, send me an email and mention the app you bought, your full name and any other email addresses the app might be licensed to. Thanks!