I need a sample program to create and sign a SegWit P2PKH testnet Bitcoin transaction on an offline computer, where I only need to fill in my private key, addresses, and other details. Thank you.

[mallcoffee123g01-bot]

I am using the Python bitcoinlib library to create an offline Native SegWit (P2WPKH) transaction. The code I’m using is as follows:

from bitcoinlib.transactions import Transaction

def create_native_segwit_offline_transaction(prev_txid, prev_output_index, prev_output_value, from_privkey_wif, to_address, send_value, network='testnet'):
tx = Transaction(network=network, witness_type='segwit')

tx.add_input(prev_txid, prev_output_index, keys=[from_privkey_wif], value=prev_output_value, witness_type='segwit')

tx.add_output(send_value, to_address)

tx.sign()

return tx.as_hex()
範例使用

prev_txid = 'b759ffc1c3b85814ecb8f9333b6dc9329673db1cd02397612824a795a0022d18'
prev_output_index = 1
prev_output_value = 185046
from_privkey_wif = ''
to_address = 'tb1q6sjp8reaa7l0lyh4ey7a8l52p0nzd3wq5cmsqd'
send_value = 1000

raw_tx_hex = create_native_segwit_offline_transaction(prev_txid, prev_output_index, prev_output_value, from_privkey_wif, to_address, send_value)
print(raw_tx_hex)

The transaction raw hex generated by this code is:
01000000000101182d02a095a72428619723d01cdb739632c96d3b33f9b8ec1458b8c3c1ff59b70100000000ffffffff01e803000000000000160014d424138f3defbeff92f5c93dd3fe8a0be626c5c002483045022100f4822975e7fe1bd25d38df2d3b65ef9055469c607cf9612fe45572f4e4a1237e02200faf8900619fdb8ab8d879bbc80215f72a6017626f78320485bb976df6e56c1a012103d3ccd12e773aa7dbce382dd0d373c1ca916a9809b4073851bdc3c7eedb80081700000000

However, after broadcasting it to a testnet node, I received an error from the node:
Failed to broadcast transaction, reason: bad-txns-inputs-missingorspent

Problem:

I have confirmed the following:

The prev_txid and prev_output_index correspond to a valid UTXO that exists and is unspent on the blockchain.

The prev_output_value matches the value of that UTXO.

The private key is in correct WIF format, and it corresponds to the address that holds the UTXO.

The transaction format (hex) appears valid and follows the Native SegWit specification.

My Question:

What could be the possible cause of this error?

Is there anything missing or incorrect in my code?
Do I need to explicitly provide additional parameters such as the previous scriptPubKey, or take any other steps to ensure that the transaction is accepted and broadcasted by the node?

🔍Additional Info:

I have used the native bitcoinlib methods to construct the transaction.

I have included the UTXO value and specified witness_type='segwit'.

However, the add_input() function in bitcoinlib does not seem to accept script_pub_key as a parameter.

So my questions are:

Do I need to provide the previous output’s scriptPubKey in another way?

Or should I use a different tool to verify whether the signature in the transaction is valid?

Any guidance would be greatly appreciated — thank you!

[mccwdev]

The previous transaction (b759ffc1c3b85814ecb8f9333b6dc9329673db1cd02397612824a795a0022d18) does not seem to exists, so it gives an error that the utxo cannot be found (bad-txns-inputs-missingorspent)

[mallcoffee123g01-bot]

The transaction (b759ffc1c3b85814ecb8f9333b6dc9329673db1cd02397612824a795a0022d18) exists, so why can I still not create and sign the transaction? Thank you.

[mallcoffee123g01-bot]

The transaction (b759ffc1c3b85814ecb8f9333b6dc9329673db1cd02397612824a795a0022d18) is on testnet 4.

[mccwdev]

After you made changes to a transaction, for example with add_input or add_output, you need to update it.

You could use the sign_and_update() method. With tx.verify() the transaction will be verified, I don't think this step is required, but it good to check before you try to push the transaction to the network.

Also in your code example the 'testnet4' was not passed to the method, so I think the default 'testnet' was used.

With the code below I got it working

# Create private key, and send btc to address
phrase = 'term teach tunnel candy pledge student acoustic robust total flash marine sound'
k = HDKey().from_passphrase(phrase, network='testnet4')

def create_native_segwit_offline_transaction(prev_txid, prev_output_index, prev_output_value, from_privkey_wif, to_address, send_value, network='testnet'):
    tx = Transaction(network=network, witness_type='segwit')

    tx.add_input(prev_txid, prev_output_index, keys=[from_privkey_wif], value=prev_output_value, witness_type='segwit')

    tx.add_output(send_value, to_address)

    tx.sign_and_update()
    tx.verify()

    return tx.as_hex()

network = 'testnet4'
prev_txid = 'c76d6d3604e1be48a3e02fb73bfbbf70efd80467a0f06a3727e5147e6448a9aa'
prev_output_index = 1
prev_output_value = 10000
from_privkey_wif = k
to_address = 'tb1qhk3f5p3hs2a3lvgfmfrtjnfczj7g0tq9kc27kc'
send_value = 9000

raw_tx_hex = create_native_segwit_offline_transaction(prev_txid, prev_output_index, prev_output_value,
                                                      from_privkey_wif, to_address, send_value, network)
print(raw_tx_hex)

See https://blocksmurfer.io/tbtc4/transaction/fedec6b0ace1e955abd671d3111e1fdcde16abbfefc9001f4cb3ffa62292a9b0