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Polymarket errors / Pricing
400 Bad RequestDon't retry

Invalid side

The `side` parameter must be `BUY` or `SELL`.

side must be BUY or SELL.

Retry? Don't retry

Sending the same request again returns the same error. Change the request first.

Returned by

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 "Invalid side" in msg:
        raise ValueError(msg)  # fix the request, don't retry

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.