How can I resolve the CALL_EXCEPTION error when fetching a WETH/USDC quote on Sepolia using ethers v6?

Below is a checklist addressing the common causes of a CALL_EXCEPTION in your context along with a corrected code snippet:

---

1. Use callStatic Instead of .staticCall

In ethers v6, the typical pattern for executing read-only (static) calls is to use the contract’s callStatic property. Change this line:

JSCopied
const amountOut = await quoterContract.quoteExactInputSingle.staticCall(
  tokenIn,
  tokenOut,
  fee,
  formattedAmount,
  0
);

to:

JSCopied
const amountOut = await quoterContract.callStatic.quoteExactInputSingle(
  tokenIn,
  tokenOut,
  fee,
  formattedAmount,
  0
);

---

2. Verify Contract Addresses on Sepolia

Make sure that the addresses you have in your config are correctly deployed on the Sepolia testnet. A typical error from the quoter is if the contract at the given address does not implement the expected function (or isn’t deployed at all). Double-check:

• config.QUOTER_ADDRESS
• config.UNISWAP_FACTORY
• Token addresses for config.WETH and config.USDC

---

3. Confirm ABI Accuracy

Your ABI for the quoter appears to match the expected interface:

JSCopied
const QUOTER_ABI = [
  "function quoteExactInputSingle(address,address,uint24,uint256,uint160) external returns (uint256)"
];

This is the correct ABI for querying a Uniswap V3 quoter. If the deployed contract on Sepolia does have a different interface then you would need to adjust the ABI accordingly.

---

4. Example of the Corrected Code Snippet

Below is the modified snippet incorporating the changes:

JAVASCRIPTCopied
import { ethers } from 'ethers';
import dotenv from 'dotenv';
dotenv.config();

console.log('Starting detection bot...');

// ABI for the Quoter
const QUOTER_ABI = [
  "function quoteExactInputSingle(address,address,uint24,uint256,uint160) external returns (uint256)"
];

const UNISWAP_FACTORY_ABI = [
  "function getPool(address,address,uint24) external view returns (address)"
];

const config = {
  SEPOLIA_RPC_URL: process.env.SEPOLIA_RPC_URL,
  UNISWAP_FACTORY: "0x0227628f3F023bb0B980b67D528571c95c6DaC1c",
  QUOTER_ADDRESS: "0xEd1f6473345F45b75F8179591dd5bA1888cf2FB3",
  WETH: "0xfff9976782d46cc05630d1f6ebab18b2324d6b14",
  USDC: "0x94a9d9ac8a22534e3faca9f4e7f2e2cf85d5e4c8",
  MIN_PROFIT_ETH: 0.05,
  GAS_LIMIT: 1_000_000
};

const provider = new ethers.JsonRpcProvider(config.SEPOLIA_RPC_URL);

const quoterContract = new ethers.Contract(
  config.QUOTER_ADDRESS,
  QUOTER_ABI,
  provider
);

const uniswapFactory = new ethers.Contract(
  config.UNISWAP_FACTORY,
  UNISWAP_FACTORY_ABI,
  provider
);

async function main() {
  // Verify pool existence first
  const poolAddress = await uniswapFactory.getPool(
    config.WETH,
    config.USDC,
    3000
  );
  
  console.log(`WETH/USDC 0.3% pool address: ${poolAddress}`);
  if (poolAddress === ethers.ZeroAddress) {
    throw new Error("WETH/USDC 0.3% pool does not exist on Sepolia");
  }

  provider.on('block', async (blockNumber) => {
    console.log(`Scanning block ${blockNumber}...`);
  
    try {
      const [price1, price2] = await Promise.all([
        getPoolPrice(config.WETH, config.USDC, 3000, '0.001'),
        getPoolPrice(config.USDC, config.WETH, 3000, '0.001')
      ]);

      console.log(`Price1: ${price1}, Price2: ${price2}`);
      
      const profit = (price1 * price2) - 1;
      if (profit > config.MIN_PROFIT_ETH) {
        console.log(`Opportunity found! Profit: ${profit.toFixed(4)} ETH`);
        console.log("Sending transaction....");
      }
    } catch (error) {
      console.error('Block processing error:', error.message);
    }
  });
}

async function getPoolPrice(tokenIn, tokenOut, fee, amountIn) {
  console.log(`Checking price for ${tokenIn} -> ${tokenOut}`);

  try {
    const decimals = tokenIn === config.WETH ? 18 : 6;
    const formattedAmount = ethers.parseUnits(amountIn.toString(), decimals);
    
    // Use callStatic here
    const amountOut = await quoterContract.callStatic.quoteExactInputSingle(
      tokenIn,
      tokenOut,
      fee,
      formattedAmount,
      0
    );

    console.log(`Price check: ${tokenIn}->${tokenOut} = ${ethers.formatUnits(amountOut, 6)}`);
    return parseFloat(ethers.formatUnits(amountOut, 6));
  } catch (error) {
    console.error(`Price check failed: ${error}`);
    return 0;
  }
}

main().catch(error => {
  console.error('Fatal error:', error);
  process.exit(1);
});

---

Summary

• Replace .staticCall with .callStatic for read-only contract calls.
• Ensure all contract addresses and network configurations are correct for Sepolia.
• The provided ABI for the quoter is correct (assuming the on-chain contract matches the interface).

This should help resolve the CALL_EXCEPTION error you encountered when fetching the quote using ethers v6 on Sepolia.