Hi James, sorry to hear you’re having trouble with the extension. Unfortunately Linux isn’t officially supported because I don’t have a way to reliably test the extension in multiple distros. Typically the “unexpected end of input” error is thrown by Aseprite itself when it runs into an issue parsing JSON.
As for the “invalid palette name”, that’s tricker because the daily palette is parsed directly from here: https://lospec.com/palette-list/current-daily-palette.txt and should (barring an issue with Lospec itself) always be valid.
If you paid for the extension, please let me know so I can see about issuing a refund.