Hello, really late reply, but I just want to clarify what this is, since I have yet to release a response. Genuinely, these issues occur when there is a server error at the host, which in turn, makes for an error message like the one you see in this picture.
The error message is stating that the Rest API has failed to respond with a response, and the json parse has failed at making sense of the data, which is likely a cloudflare error page or error 500 page.
The old API is very unstable, which is why it’s undergoing a remake. I call it “Pluton” and I will open-source it. It’s going to be much more stable, and the launcher itself will also be vastly more usable.