order couldn't be fully filled. FOK orders are fully filled or killed.
A Fill-or-Kill order could not be completely filled by available liquidity. The entire order is rejected.
A fill-or-kill order found less liquidity than it needed, so none of it filled. Use a smaller size, a limit order, or FAK if partial fills are acceptable.
Retry? Don't retry
Sending the same request again returns the same error. Change the request first.
Any authenticated CLOB endpoint can return this.
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 "order couldn't be fully filled. FOK orders are fully filled" in msg:
raise ValueError(msg) # fix the request, don't retryRelated errors
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.