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This guide walks through the full workflow of placing a trade — from finding a market to executing an order and monitoring the result.

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Find a Market

Before placing a trade, you need the token ID for the outcome you want to trade. How you get it depends on the venue.

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Polymarket

Use the List Markets endpoint to browse active markets: 
import requests

HEADERS = {"x-api-key": "YOUR_API_KEY"}

# Find top markets by volume
markets = requests.get(
    "https://api.predexon.com/v2/markets",
    headers=HEADERS,
    params={"status": "active", "sort": "volume", "limit": 5}
).json()

for market in markets["markets"]:
    print(f"{market['question']}")
    for outcome in market["outcomes"]:
        print(f"  {outcome['label']}: tokenId={outcome['tokenId']}")
Each outcome (e.g., “Yes” and “No”) has its own tokenId. You’ll pass this token ID when placing an order.

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Predict.fun

Find markets on Predict.fun or via the Predict.fun API. You’ll need two identifiers:
  • marketId — the numeric market ID (e.g., "46954")
  • tokenId — the on-chain outcome token ID (a large numeric string)

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Understand the Identifiers

Every order requires you to tell the API which outcome you’re trading. There are two ways to do this:

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Option 1: Explicit fields

Pass venue, tokenId, and (for Predict) marketId separately: 
{
  "venue": "polymarket",
  "tokenId": "71321045679252212...",
  "side": "buy",
  "type": "market",
  "amount": "10"
}

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Option 2: Market identifier

Use the composite marketIdentifier string, which is returned in every order and position response: 
{
  "marketIdentifier": "polymarket:71321045679252212...",
  "side": "buy",
  "type": "market",
  "amount": "10"
}
The format is polymarket:<tokenId> or predict:<marketId>:<tokenId>. This is convenient when re-trading a market you’ve already interacted with — just reuse the marketIdentifier from a previous response.

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Choose Your Order Type

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Market orders

Execute immediately at the best available price. Use these when you want to get in or out of a position right now.
  • Market BUY — you specify amount (how much USDC.e/USDT to spend). The API fills as many shares as possible at the current price.
  • Market SELL — you specify size (how many shares to sell). The API sells them at the best available price.

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Limit orders

Sit on the orderbook at a specific price until someone takes the other side. Use these when you have a target price in mind and are willing to wait.
  • Limit BUY — you specify size (shares) and price (per share). The order rests until a seller matches it.
  • Limit SELL — same as limit buy, but on the sell side.

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Understand Amount vs Size vs Price

This is the most common source of confusion. The rule is simple:
  • amount = stablecoin to spend (USDC.e or USDT). Only used for market BUY orders.
  • size = number of shares. Used for everything else (market sell, all limit orders).
  • price = price per share. Only used for limit orders.
Order Typeamountsizeprice
Market BUYRequiredRejected—
Market SELLRejectedRequired—
Limit BUYRejectedRequiredRequired
Limit SELLRejectedRequiredRequired
Sending the wrong field returns a 400 error with a message indicating which field is expected.

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Place an Order

All orders go to the same endpoint: POST /api/users/{userId}/orders. See the reference for Polymarket or Predict.

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Polymarket example

import requests

user_id = "YOUR_USER_ID"
HEADERS = {"x-api-key": "YOUR_API_KEY", "Content-Type": "application/json"}
BASE = "https://trade.predexon.com"

# Market buy — spend $10 USDC.e on "Yes" shares
order = requests.post(
    f"{BASE}/api/users/{user_id}/orders",
    headers=HEADERS,
    json={
        "venue": "polymarket",
        "tokenId": "71321045679252212...",
        "side": "buy",
        "type": "market",
        "amount": "10"
    }
).json()

print(f"Status: {order['status']}")
print(f"Shares received: {order['sizeMatched']}")

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Predict.fun example

# Market buy — spend 10 USDT on "Nuggets" shares
order = requests.post(
    f"{BASE}/api/users/{user_id}/orders",
    headers=HEADERS,
    json={
        "venue": "predict",
        "tokenId": "103210916722172...",
        "marketId": "46954",
        "side": "buy",
        "type": "market",
        "amount": "10.00"
    }
).json()

print(f"Status: {order['status']}")
print(f"Shares received: {order['sizeMatched']}")

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Limit order example

# Place a limit buy at $0.40 per share on Polymarket
order = requests.post(
    f"{BASE}/api/users/{user_id}/orders",
    headers=HEADERS,
    json={
        "venue": "polymarket",
        "tokenId": "71321045679252212...",
        "side": "buy",
        "type": "limit",
        "size": "20",
        "price": "0.40"
    }
).json()

# Limit orders return status "open" — they sit on the orderbook
print(f"Status: {order['status']}")  # "open"
print(f"Order ID: {order['orderId']}")

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Venue Differences

The two venues have different constraints and behaviors:
PolymarketPredict.fun
BlockchainPolygonBSC
CollateralUSDC.eUSDT (BEP-20)
Price rangeBetween 0 and 1 (exclusive)Between 0 and 1 (exclusive)
Min market order> 1 USDC.e~$0.90 USDT
Min limit order> 5 shares~$0.90 USDT
Extra field—marketId required
FeesConfigurable partner feeExchange fee that varies by market (automatic)

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After Placing an Order

Once your order is placed, you can:

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Next Steps

Funding & Withdrawals

Learn how to deposit and withdraw funds

Fees & Monetization

Set up partner fees to monetize your app

Place Order Reference

Full endpoint reference for placing orders

Get Positions Reference

Full endpoint reference for positions