I have just downloaded a version of that plugin successfully in two different ways (one using AltUI, and the other with openLuup directly. I am using the latest development version of openLuup, which I suggest you upgrade to.)
I just manually upgraded to the latest development version as nothing was updating via the plugin UI in the version I was using (20.2.26). After installing all the files in the latest development branch, the App store is now working as expected. Not sure what was going on there, but the log entries are accurate.
What I meant by “parsing” is that if I go directly to the link, the JSON displayed in my browser without any errors.
OK. The JSON error has nothing to do with the download files. The problem arises from some changes which GitHub has made, specifically the redirection of some URLs which the LuaSocket library is not able to handle. The latest development version has a workaround for this, so this shouldn’t happen again (for a while, at least!)
The HTTP error is something different again, but may just be a transient issue. Or do you see it regularly in the log?