AppImages require a working FUSE installation - libfuse, fusermount, /dev/fuse with proper permissions, etc.
This should be the default in most desktop distributions, but might not be available on your server. If you have root rights on your server, you can install fuse and it should work.
If you do not have root rights on your server, you could unpack the AppImage (it is an ISO file really), and use the resulting AppDir, which does not need FUSE. Just run the "AppRun" file inside the unpacked AppImage.
If you like PortableLinuxApps and the AppImage format, you might consider a donation -->