Here is an article that explains what the error “non-mandatory-script-verify-flag (Witness program hash mismatch)” means and why you might be seeing it when trying to send a raw signed transaction using Bitcoinlib:

Understanding the Error: Non-Mandatory Script Verify Flag

When sending raw transactions in Bitcoin, you need to ensure that all required flags are included. One of these mandatory flags is the script-verify flag, which allows the transaction script (the code that performs various operations on the input) to be verified. However, there’s a catch – some scripts rely on specific witness program hashes being present.

What Causes the Error?

The error “non-mandatory-script-verify-flag (Witness program hash mismatch)” typically occurs when the script-verify flag is not included in the transaction script. This can happen if your code doesn’t properly handle witness programs or if there are dependencies between scripts that aren’t met.

What Does it Mean?

When a transaction is sent, Bitcoin checks several flags to ensure everything is valid and functional. The script-verify flag is crucial for this process because certain transactions rely on specific witness program hashes being present in the script. If these hashes don’t match, the transaction may be rejected.

Simplified Example Code:

Here’s a simplified example of how you might create a transaction using Bitcoinlib:

from bitcoinlib.transactions import Output, Key











Create a key for the sender

sender_key = Key.from_str("my-sender-key", "hex")



Define the output script (a simple example)

output_script = "0c6f1d2c6e8b76e42f8..."



Create an input script that relies on a specific hash program witness

input_script = "0b95fa7f3e4daeb5d34..."


def slim():

    
Create the output and input scripts

    output_output = Output.from_str("0c6f1d2c6e8b76e42f8...", sender_key, "hex", None) 
No script-verify flag

    input_input = Input.from_str(input_script, sender_key, "hex")


    
Send the transaction

    tx_hash = bitcoinlib.utils.hash(output_output)

    print(f"Transaction hash: {tx_hash}")


if __name__ == "__main__":

    slim()

Conclusion

In this example, we created a simple transaction with multiple outputs and inputs. However, when sending this transaction using Bitcoinlib, the error “non-mandatory-script-verify-flag (Witness program hash mismatch)” occurred because the script-verify flag was missing from one of the input scripts.

Best Practices:

To avoid similar issues in the future:

• Always include the script-verify flag in your transaction script.

• Ensure that all witness program hashes are present and correct.

• Consider adding dependencies between scripts to minimize the risk of errors.

By following these best practices, you can ensure that your transactions pass validation and avoid receiving any error messages like “non-mandatory-script-verify-flag (Witness program hash mismatch)”.

ETHEREUM ISSUE HELP NEEDED