nautechsystems/nautilus_trader · error

Router allowance for token {token} is already {}; approve ze

Error message

Router allowance for token {token} is already {}; approve zero before setting a new nonzero allowance

What it means

Allowance guard before approving a router spend: a nonzero allowance already exists for the token/spender pair; setting a new nonzero allowance directly is race-prone, so an approve-to-zero step is required first.

Source

Thrown at crates/adapters/blockchain/src/execution/client.rs:2630

                    spender: router,
                }
                .abi_encode();
                let allowance = required_verification(
                    self.verification
                        .verify_decoded_call(
                            None,
                            &token,
                            U256::ZERO,
                            &allowance_call,
                            block,
                            |result| {
                                ERC20::allowanceCall::abi_decode_returns(result).map_err(Into::into)
                            },
                        )
                        .await,
                    "pre-sign router allowance",
                )?;
                anyhow::ensure!(
                    allowance.value.is_zero() || amount.is_zero(),
                    "Router allowance for token {token} is already {}; approve zero before setting a new nonzero allowance",
                    allowance.value
                );

                let approve_call = ERC20::approveCall {
                    spender: router,
                    amount,
                }
                .abi_encode();
                let simulation = required_verification(
                    self.verification
                        .verify_decoded_simulation(
                            &self.wallet_address,
                            &token,
                            U256::ZERO,
                            &approve_call,
                            block,

View on GitHub (pinned to 18893faf8b)

Solutions

  1. Approve zero first, then set the new allowance
  2. Reuse the existing sufficient allowance if it covers the intended spend
Defensive patterns

Strategy: validation

When it happens

Trigger: Thrown at crates/adapters/blockchain/src/execution/client.rs:2630 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/29a35463a58d1d84. Report an issue: GitHub.