Place Order

POST /v1/accounts/{accountId}/orders

Place a buy or sell order. The user does not specify a venue — Predexon routes. Request

{
  "predexonId": "px-abc123def456",
  "side": "buy",
  "type": "market",
  "amount": 50.00
}

Field	Type	Description
`predexonId`	string	Canonical outcome identifier from the Data API. Each outcome (Yes / No) has its own `predexonId` — there is no separate `outcome` field on the request.
`side`	`"buy"` \| `"sell"`
`type`	`"limit"` \| `"market"`
`size`	number	Number of shares.
`amount`	number	USDC notional.
`price`	number	Limit price, strictly between 0 and 1 (exclusive).

size, amount, and price are conditionally required by order type:

Order type	Required	Rejected
Limit BUY / SELL	`size`, `price`	`amount`
Market BUY	`amount`	`size`, `price`
Market SELL	`size`	`amount`, `price`

Response 201 Created Market orders fill atomically — the response shows the executed fill. For a limit order that doesn’t fill immediately, status is "open", filled is "0", averagePrice is null, and metadata.fills is empty until fills arrive. Use Get Order or List Trades to inspect post-placement state.

{
  "orderId": "ord_3e2b...",
  "predexonId": "px-abc123def456",
  "title": "Will Trump win the 2028 election?",
  "outcome": "Yes",
  "side": "buy",
  "type": "market",
  "status": "filled",
  "filled": "100",
  "averagePrice": "0.495",
  "amount": "50.00",
  "notional": "49.50",
  "fee": "0.50",
  "createdAt": "2026-05-06T12:00:00.214Z",
  "filledAt": "2026-05-06T12:00:00.832Z",
  "metadata": {
    "fills": [
      { "source": "venue", "venue": "polymarket", "size": "50", "fillPrice": "0.50", "fee": "0.25" },
      { "source": "venue", "venue": "limitless", "size": "50", "fillPrice": "0.49", "fee": "0.25" }
    ]
  }
}

The top-level fields (status, filled, averagePrice, notional, fee) are the aggregated source of truth. metadata.fills shows the per-source breakdown so users can verify routing and reconcile against on-chain activity. Math: 50 × $0.50 + 50 × $0.49 = $49.50 notional + $0.50 fees = $50 = amount; avg $0.495. Trading fees on venue fills are venue-passthrough: top-level fee is the sum of metadata.fills[].fee. RFQ fills carry no explicit fee (the market maker’s compensation is baked into the quoted fillPrice). A fill from a market maker looks like this — source: "rfq" with a marketMaker identifier instead of venue:

{ "source": "rfq", "marketMaker": "mm-acme", "size": "50", "fillPrice": "0.495", "fee": "0" }

See Liquidity sources for how the router decides between venue order books and RFQ market makers. There is no modify endpoint — to change a price or size on an open limit order, cancel it and place a new one.

Status values

Status	Meaning
`open`	Limit order accepted, awaiting fills (or partially filled).
`filled`	Fully filled.
`cancelled`	Cancelled before fully filling. The filled portion (if any) remains as a position.
`expired`	Limit order reached its time-in-force expiry without fully filling.
`pending`	Transitional — order is being submitted to venues but not yet acknowledged.
`failed`	Submission rejected after acceptance (e.g., no venue had usable liquidity, treasury error).

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Concepts

API Reference

Status values

​Status values

Status values