Sorry you’re encountering issues. I had tested on Linux when developing this but it could be anything specific to your configuration. Is the directory it would save to set with permissions for the script to be able to perform a write? If you included a screenshot of your error it appears to not have attached.
Basically the error says that the write of the file has failed, i checked the Aseprite API docs and appears that now directories need a slash at the start of them in linux and MacOS, i wouldn't be surprised if this change has the fault of it, but in case that are the permissions instead of the script, i need to see how to change them