From my testing, the forge fetch does not support plain HTTP, only HTTPS. I get HTTP 400 errors when I try to fetch from a plain ‘http’ URL. It works for HTTPS.
I doubt its a problem for many real work use case. However:
Its nowhere documented as far as I know: It is documented here: https://developer.atlassian.com/platform/forge/function-reference/nodejs-runtime/#https-only- If its HTTP by accident, you get the HTTP 400 errors without extra information what is wrong.