400 Bad RequestDon't retry
'{address}' address in closed only mode
The Polymarket CLOB API returns this with HTTP 400. Polymarket doesn't document a cause beyond the message.
Retry? Don't retry
Sending the same request again returns the same error. Change the request first.
Returned by
- POST /order 5,000 req / 10s
Handling it in code
The CLOB API returns errors as {"error": "..."}. It also rewrites status codes by message, so branch on the text: anything containing "not found" becomes 404 and anything containing "unauthorized" becomes 401.
r = session.post(url, json=payload, headers=headers)
if r.status_code >= 400:
msg = r.json().get("error", "")
if "address in closed only mode" in msg:
raise ValueError(msg) # fix the request, don't retryRelated errors
- 400Invalid order payload
- 400the order owner has to be the owner of the API KEY
- 400the order signer address has to be the address of the API KEY
- 400'{address}' address banned
- 503Trading is currently cancel-only. New orders are not accepted, but cancels are allowed.
- 503post-only mode: only post-only orders and cancels are allowed
For errors Polymarket doesn't document, like "order manager not ready" or 403s from the edge, see the full error guide.
Message and status from Polymarket's error reference, synced 2026-10-04.