nautechsystems/nautilus_trader · error

Polymarket collateral-sized limit BUY price must be positive

Error message

Polymarket collateral-sized limit BUY price must be positive

What it means

`build_limit_order_from_collateral` builds a collateral-sized (quote-amount) limit BUY order for Polymarket. Polymarket CLOB orders are price*amount based, so a non-positive price would produce zero or negative maker/taker amounts. `anyhow::ensure!` rejects any price <= 0 with this message before computing order amounts.

Source

Thrown at crates/adapters/polymarket/src/execution/order_builder.rs:156

            neg_risk,
        )
    }

    /// Builds and signs a collateral-sized limit BUY for submission.
    ///
    /// `amount` is the pUSD collateral to spend. The signed maker amount is the collateral after
    /// venue-required cent quantization, and the taker amount is the share quantity derived from
    /// that exact signed amount.
    pub(crate) fn build_limit_order_from_collateral(
        &self,
        token_id: &str,
        price: Decimal,
        amount: Decimal,
        expiration: &str,
        neg_risk: bool,
        tick_decimals: u32,
    ) -> anyhow::Result<PolymarketOrder> {
        anyhow::ensure!(
            price > Decimal::ZERO,
            "Polymarket collateral-sized limit BUY price must be positive"
        );

        let (maker_amount, taker_amount) =
            compute_quote_buy_maker_taker_amounts(price, amount, tick_decimals);
        anyhow::ensure!(
            maker_amount > Decimal::ZERO,
            "Polymarket collateral-sized limit BUY amount {} pUSD truncates to zero at {LOT_SIZE_SCALE} decimal places",
            amount.normalize(),
        );
        anyhow::ensure!(
            taker_amount > Decimal::ZERO,
            "Polymarket collateral-sized limit BUY derives a zero share quantity"
        );
        anyhow::ensure!(
            taker_amount * price == maker_amount,
            "Polymarket collateral-sized limit BUY amount {} pUSD cannot preserve limit price {} after venue quantization",

View on GitHub (pinned to 18893faf8b)

Solutions

1. Ensure the order price is positive before submission; fetch/refresh market data so a real last/best price is available
2. Validate the instrument's price precision/tick_decimals config so prices don't round to zero
3. Guard the strategy to skip the order when no valid price exists
4. Check Decimal scale/rounding upstream that could reduce a small price to 0

Example fix

// before
let order = client.build_limit_order_from_collateral(
    OrderSide::Buy, price_from_stale_feed, amount, ...)?;
// after
anyhow::ensure!(price_from_stale_feed > Decimal::ZERO, "no valid price");
let order = client.build_limit_order_from_collateral(
    OrderSide::Buy, price_from_stale_feed, amount, ...)?;

use rust_decimal::Decimal;
fn validate_buy_price(price: Decimal) -> Result<(), String> {
    if price <= Decimal::ZERO { Err(format!("price must be positive, got {price}")) } else { Ok(()) }
}

match adapter.submit_order(order).await {
    Err(e) if e.to_string().contains("price must be positive") => {
        tracing::warn!("skipping order with invalid price");
    }
    other => other?,
}

When it happens

Trigger: Submitting a market BUY order that internally converts to a limit order when the computed/last price is 0 (e.g. no market data available); passing price=0 or a negative Decimal directly through the order path; a bug or division-by-zero upstream yielding 0 price.

Common situations: Trading a thin/illiquid market where best bid/ask is missing so derived price is 0; instrument configured with wrong tick/price precision causing rounded-to-zero prices; feeding a strategy unvalidated prices before adapter submission.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• fee rate must be non-negative
• fee price must be in [0, 1]
• market amount must be positive
• market-book size must be non-negative
• {field} {value} must be greater than zero and less than one

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/b759478629d219e3. Report an issue: GitHub.