invalid market-buy price {price}: must satisfy 0 < price < 1

Error message

invalid market-buy price {price}: must satisfy 0 < price < 1 for fee adjustment

What it means

adjust_market_buy_amount applies Polymarket's fee curve to a market-buy amount, and that math is only defined for prices strictly between 0 and 1 (a binary-market outcome probability). The function bails out when the supplied price is zero, negative, or >= 1, since fees at such prices are meaningless or non-finite.

Source

Thrown at crates/adapters/polymarket/src/execution/parse.rs:518

/// `price` must be strictly inside `(0, 1)`. The SDK relies on its
/// order-builder pipeline to enforce this. Because [`adjust_market_buy_amount`]
/// is public, it repeats the precondition here.
///
/// # Errors
///
/// Returns an error if `price` is outside the open `(0, 1)` interval, or if
/// amount or balance is non-positive, a fee input is negative, arithmetic overflows,
/// or the adjusted amount truncates to zero.
pub fn adjust_market_buy_amount(
    amount: Decimal,
    user_pusd_balance: Decimal,
    price: Decimal,
    fee_rate: Decimal,
    fee_exponent: Decimal,
    builder_taker_fee_rate: Decimal,
) -> anyhow::Result<Decimal> {
    if price <= Decimal::ZERO || price >= Decimal::ONE {
        anyhow::bail!(
            "invalid market-buy price {price}: must satisfy 0 < price < 1 for fee adjustment",
        );
    }

    let platform_fee_rate = fee_curve_rate(fee_rate, price, fee_exponent)?;

    anyhow::ensure!(amount > Decimal::ZERO, "market-buy amount must be positive");
    anyhow::ensure!(
        user_pusd_balance > Decimal::ZERO,
        "market-buy balance must be positive"
    );
    anyhow::ensure!(
        builder_taker_fee_rate >= Decimal::ZERO,
        "builder fee rate must be non-negative"
    );
    let platform_fee = amount
        .checked_div(price)
        .and_then(|shares| shares.checked_mul(platform_fee_rate))

View on GitHub (pinned to 18893faf8b)

Solutions

Verify the price is a Decimal in (0, 1) before calling; divide by 100 if it came from a percentage source.
Check the source of the price (book level, manual input) — reject empty or degenerate books earlier via calculate_market_price.
For markets priced at ~0 or ~1, treat the order as invalid and surface a user-facing validation error instead of calling the fee adjustment.
Add a unit test pinning boundary behavior at price=0, 1, and just inside the range.

Example fix

// before
let price = Decimal::from(55); // percent, not decimal
let amount = adjust_market_buy_amount(balance, price, fee_rate, fee_exponent, builder_taker_fee_rate)?;
// after
let price = Decimal::from(55) / Decimal::from(100); // 0.55
anyhow::ensure!(price > Decimal::ZERO && price < Decimal::ONE, "price must be in (0, 1)");
let amount = adjust_market_buy_amount(balance, price, fee_rate, fee_exponent, builder_taker_fee_rate)?;

Defensive patterns

Strategy: validation

Validate before calling

if price <= Decimal::ZERO || price >= Decimal::ONE {
    return Err(format!("price {price} outside (0,1); check percent-vs-decimal conversion"));
}

Type guard

fn is_valid_market_price(p: &Decimal) -> bool {
    *p > Decimal::ZERO && *p < Decimal::ONE
}

Prevention

Always represent prices as decimals in (0,1), never percentages
Validate prices at the API boundary before fee math
Test boundary conditions price=0 and price=1 in unit tests
Derive prices from calculate_market_price so books are validated first

When it happens

Trigger: Calling adjust_market_buy_amount (directly or via order building in submit-market flows) with price <= 0 or price >= 1 — typically a price derived from a stale/empty book, a percentage vs decimal unit mistake (e.g. 55 instead of 0.55), or a price of exactly 1.0 for a fully-resolved market.

Common situations: Unit-conversion bugs (feeding percent-scaled prices), best-ask fetched from a degenerate book, or submitting market buys on markets at the resolution boundary where the top-of-book price is 1.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/6eece8e1ebf86dd5. Report an issue: GitHub.