I got this error :

To fix it, just add a “s” to the http like this in the README :
"$INST_JAVA" -jar packwiz-installer-bootstrap.jar https://localhost:8080/pack.toml

I'm having this issue as of today. Super weird cause I've definitely run this before. I didn't even change my prism custom command, it's just now not working. Using https does not work for me, a different error.

Interestingly, I just on a whim tried changing the port to 8888 in both the packwiz serve command and prism and now it works. Super weird, because running a curl http://localhost:8080/pack.toml returned the file, but prism wouldnt work with it. Idk! just glad it works now.