Check the signature field of the user operation. It may be in an incompatible format.

Debugging checklist

• The user operation hash is correct
  • The user operation data matches the final user operation that is sent to the bundler client
  • The Entry Point address is correct
  • The Chain ID is correct
• The smart contract of the account expects the same type of signature (e.g., keccak256)

References

Learn more about signing user operations

Get the user operation hash