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User operation reverted

A user operation reverts with reason 0x when the validation phase passes but the execution phase fails silently. This is distinct from AA-coded EntryPoint contract errors such as AA23, AA25, or AA21.

When the EntryPoint contract calls the smart account's execution function, it uses a low-level call internally. If that inner call reverts with empty data, the bundler surfaces the error as reason 0x with no additional information.

The following are common causes.

Function doesn't exist​

The callData encodes a call from the smart account to a target contract, but the function selector doesn't match any function on that contract and no fallback function exists. The EVM reverts with empty data.

This commonly happens when:

  • The function selector has a typo or doesn't match the target's ABI.
  • The target address is wrong or points to a different contract.
  • The target contract isn't deployed on the current chain.

Solution​

Decode your callData and verify the inner call. Check that the target address has deployed code and that the function selector matches the target's ABI.

const code = await publicClient.getCode({
  address: targetAddress,
});

if (!code) {
  console.log("No contract deployed at this address");
}

Bare revert without a message​

The target contract uses require(false) or revert without a reason string. The revert returns empty data. Contracts commonly use bare reverts in access control checks, reentrancy locks, or guard functions.

Solution​

Look at the target contract's source code to identify which require or revert your call parameters could trigger.

Use Tenderly to simulate the transaction and pinpoint the exact line. See the Tenderly debugger documentation for details.

Out of gas in the inner call​

Smart accounts use a low-level call internally in their execute function. When the inner call runs out of gas, the call returns false with empty return data.

This differs from the AA95 error code, which applies when handleOps itself runs out of gas. In this case, callGasLimit might be enough for the smart account's execution overhead but not enough for the actual target contract call.

Solution​

Increase callGasLimit. If you estimate gas manually, try doubling the value. Target contracts doing complex operations often need more gas than default estimates provide.

Insufficient balance or allowance​

The inner call performs an ERC-20 transferFrom but the smart account hasn't approved the spender, or doesn't hold enough tokens. Some ERC-20 implementations use bare require statements that revert without a reason string.

Solution​

Check that the smart account has sufficient token balance and approvals for the operation.

import { erc20Abi } from "viem";

const balance = await publicClient.readContract({
  address: tokenAddress,
  abi: erc20Abi,
  functionName: "balanceOf",
  args: [smartAccount.address],
});

const allowance = await publicClient.readContract({
  address: tokenAddress,
  abi: erc20Abi,
  functionName: "allowance",
  args: [smartAccount.address, spenderAddress],
});

Manual debugging​

If the cause isn't immediately clear, follow these steps:

  1. Decode the inner call: Extract the (to, value, data) tuple from your callData to understand what the smart account executes.
  2. Use Tenderly: Simulate the user operation in Tenderly to get a full execution trace. The trace view shows the exact line where the inner call reverts.
  3. Check the basics: Verify the target has deployed code, the smart account has enough ETH and tokens, and the function selector is correct.
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