FuelLabs/fuel-core · error

Unable to add more inputs because reached the maximum…

Error message

Unable to add more inputs because reached the maximum allowed inputs limit

What it means

add_input_and_witness_and_change pushes each selected coin (or message) as an input and then verifies the tx is still within tx_params.max_inputs. The error means the coin just added to satisfy a required balance or the fee pushed the input count over the chain limit.

Solutions

1. Consolidate dust UTXOs for the fee account and each required asset into fewer, larger coins
2. Lower the fee pressure: reduce tip/gas price, drop reserveGas, or shrink script gas usage so fewer coins are needed
3. Split the operation across multiple transactions so each stays within max_inputs

Example fix

// before
await client.assembleTx(txBytes, { requiredBalances, reserveGas: 1_000_000, /* high gas price */ });

// after
await sweepDust(client, feeAccount); // merge dust into one coin
await client.assembleTx(txBytes, { requiredBalances, reserveGas: 0 });

// rough pre-check: coins needed for fee depend on gas price and coin sizes
const { coins } = await client.request(COINS_QUERY(feeAccount, BASE_ASSET));
const minCoinsForFee = Math.ceil(estimatedFee / Math.max(...coins.map(c => Number(c.amount)), 1));
if (tx.inputs.length + requiredBalances.length + minCoinsForFee > maxInputs) {
  throw new Error('input limit would be exceeded; consolidate first');
}

catch (e) { if (/reached the maximum allowed inputs limit/.test(e.message)) { /* consolidate wallet UTXOs, reduce reserveGas/tip, split tx */ } else throw e; }

When it happens

Trigger: Coin selection for a required balance or for fee coverage returned more coins than the remaining input slots — typically dusty base-asset coins gathered to cover gas, or many coins per asset in requiredBalances.

Common situations: Fee account paid with many micro-UTXOs so covering the fee needs >max_inputs coins; requiring spend of several assets whose balances are fragmented; exclude lists forcing selection of worse (dustier) coins.

Related errors

• Filling required balances occupies a number of inputs more…
• fee index out of bounds
• The fee address index is out of bounds
• The final fee is too big to fit into `u64`
• The transaction has more outputs than allowed by the…

AI-assisted analysis of FuelLabs/fuel-core@b9d4d170da (2026-08-16). Data as JSON: /api/errors/753ba8538a2cb30f. Report an issue: GitHub.

Appendix: source

Thrown at crates/fuel-core/src/schema/tx/assemble_tx.rs:533

        if let Some(utxo_id) = input.utxo_id() {
            self.arguments.exclude.exclude(CoinId::Utxo(*utxo_id));
        }

        if let Some(nonce) = input.nonce() {
            self.arguments.exclude.exclude(CoinId::Message(*nonce));
        }

        if let Some(asset_id) = input.asset_id(&base_asset_id) {
            self.satisfy_change_policy(*asset_id)?;
        }

        self.tx.inputs_mut().push(input);

        let max_inputs = self.arguments.consensus_parameters.tx_params().max_inputs();

        if self.tx.inputs().len() > max_inputs as usize {
            return Err(anyhow::anyhow!(
                "Unable to add more inputs \
                because reached the maximum allowed inputs limit"
            ));
        }

        Ok(())
    }

    fn satisfy_change_policy(&mut self, asset_id: AssetId) -> anyhow::Result<()> {
        if self.set_change_outputs.insert(asset_id) {
            let change_policy =
                if let Some(policy) = self.change_output_policies.get(&asset_id) {
                    *policy
                } else {
                    ChangePolicy::Change(self.fee_payer_account.owner())
                };

            match change_policy {

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