1xx Informational
100 Continue
The server has received the request headers and the client should go ahead and send the body.
What causes it
- The client sent `Expect: 100-continue` before uploading a large body, so it could be rejected on headers alone.
- curl adds this header automatically for POST bodies over 1 KB.
How to fix it
- Nothing to fix — this is normal handshake traffic.
- If a proxy chokes on it, send `Expect:` (empty) to suppress the header. In curl: `-H "Expect:"`.
At a glance
- Class
- 1xx Informational
- Reference
- RFC 9110 §15.2.1
- Standardised
- Yes
- Retry the request?
- No — fix the request