Something not working, a pack that won’t convert, or an idea for the app? I’d like to hear it.
Write to support@iamjarl.com. In the app, Help › Send Feedback… opens the same address with your app and macOS version already filled in. Nothing is sent until you press send.
If a file won’t convert or the SP-404 still says “Unsupported File”, the most useful thing to include is what the app showed for that file: the format line under its name, and any reason or warning next to it.
There’s a thread for the app on Elektronauts, and I read it: It’s 404, yo! on Elektronauts. Questions asked there help the next person with the same pack too.
The app is open source. If you’re comfortable on GitHub, you can also open an issue.