(TEMPORARY FIX)
I have the same issue as you and yes I'm on Linux and Install Aseprite through Steam.
So when I run aseprite from steam it will throw me `lospec-palette-importer.lua:344: unexpected end of input` error
After add some debug check and I found out that it logged this.
/usr/bin/curl: .../SteamLinuxRuntime/.../libcurl.so.4: version
`CURL_OPENSSL_4' not found (required by /usr/bin/curl)
That means when Aseprite (launched under Steam runtime / a sandbox) runs /usr/bin/curl it ends up picking up the runtime's libcurl which is incompatible with my system curl binary. The curl binary therefore prints an error instead of JSON, causing the JSON decode failure.
So my fix is that just run aseprite directly from the installed folder or change `Aseprite.desktop` that created from steam
to this:
[Desktop Entry]
Name=Aseprite
Comment=Play this game on Steam
Exec=/home/(your-user-name)/.local/share/Steam/steamapps/common/Aseprite/aseprite
Icon=steam_icon_431730
Terminal=false
Type=Application
Categories=Game;