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UserOp signature errors

When a bundler returns errors like:

UserOperation rejected because account signature check failed (or paymaster signature, if the paymaster uses its data as signature).
Details: Invalid UserOp signature or paymaster signature

it means simulateValidation() failed during signature checks. The failure can come from either:

  • the account signature (validateUserOp)
  • the paymaster signature (validatePaymasterUserOp)

Below are the most common causes and a quick isolation checklist.

Most Common Causes​

1) Mutating the UserOperation after signing​

If you modify any field after a signature is generated, validation fails. This often happens when:

  • You request paymaster data, then later re-estimate gas or tweak fees.
  • You re-order steps and overwrite fields (e.g., callGasLimit, maxFeePerGas) after signing.

Fix: treat the UserOperation as immutable once it is signed. If any fields change, regenerate paymaster data and re-sign.

Safe order of operations:

  1. Build the full UserOperation (all fields except signature).
  2. Request paymaster data (sets paymasterAndData).
  3. (Optional) estimate gas before signing, but do not mutate afterwards.
  4. Sign and send.

2) EntryPoint version mismatch (v0.6 vs v0.7)​

EntryPoint v0.7 introduces a packed user operation format. If your account/paymaster expects one format but your tooling signs the other, the hash will differ and validation fails.

Check:

  • EntryPoint address and version on the target chain.
  • Whether your SDK/client is generating legacy UserOperation or PackedUserOperation.
  • That the same EntryPoint address/version is used when hashing and validating.

3) Paymaster signature formatting​

Many paymasters embed their signature inside paymasterAndData with a strict byte layout. Re-encoding or truncating that data breaks validation.

Fix: treat paymasterAndData as opaque bytes unless you fully control the paymaster contract and encoding.

4) Signing the wrong hash or domain​

Common causes include:

  • wrong chain ID
  • wrong EntryPoint address in the hash domain
  • wrong signer (EOA vs session key vs module key)
  • mismatched signing method (EIP-712 vs personal_sign expectations)

Sanity check: log the exact userOpHash that your client signs and compare it to the on-chain value in validateUserOp.

Fast Isolation Checklist​

  1. Try without a paymaster.
    • Set paymasterAndData = 0x and fund the smart account or EntryPoint deposit.
    • If it works → paymaster signature/formatting or mutation is the culprit.
    • If it still fails → account signature or hashing is wrong.
  2. Confirm no field mutations after paymaster data.
  3. Verify EntryPoint version and user op packing.
  4. Compare hashes end-to-end.

Notes on Gas Settings​

Low fee values typically cause inclusion issues rather than signature failures. However, many paymaster flows recalculate or replace gas fields, and if you mutate those after paymaster signing, you will invalidate the paymaster signature. In that case, request paymaster data again and re-sign.