HTTP 100 — Continue
1xx Informational
What it means
The client sent an Expect: 100-continue header and the server is telling it to go ahead and send the request body.
What to do about it
Nothing to fix — this is a normal handshake used to avoid uploading a large body that would be rejected anyway.
Where it sits
100 belongs to the 1xx family: The request was received and the process is continuing. These are rarely seen by application code.
HTTP/1.1 100 ContinueChecking it yourself
# see the status code and headers only
curl -sI https://example.com/path
# follow redirects and print each hop
curl -sIL -o /dev/null -w "%{http_code} %{url_effective}\n" https://example.com/path
# JavaScript
const r = await fetch(url);
console.log(r.status, r.statusText);