Error Validating Segwit Transactions using Python Blockcypher API: Error Running Input Script

As the title states, I’m trying to send a Litecoin transaction using the Blockcypher API Python SDK, and using Bitcoinlib for key management. I have extensively reviewed the documentation and source code for the tools I’m working with, and I have tried researching this specific error but still have yet to get past this roadblock.

I’ve gotten to a point where the transaction is built and and signatures are created, but when I try broadcasting it, the API returns this error to my console:

{'errors': [{'error': 'Error validating generated transaction: 
Error running script for input 0 referencing 79d841bf41ead0e4ecbb58197c289ec9cc087e85cf1a98196e2e415b8990357a at 0:
Script was NOT verified successfully.'}], 

'tx': {'block_height': -1, 'block_index': -1, 
'hash': 'f2ae95498b3b209ee077ad8a32292a0461ab2d37b807a647520aee31e9c62d29', 
'addresses': ['ltc1q7nyvlc6jkznpemw3g0n8f3z5z4eatfhevy07au', 'ltc1qxdvtqt9tm7rwplk8upezujtjsh6k3l85tw39ue'], 
'total': 98100, 
'fees': 1900, 
'size': 221, 
'vsize': 140, 
'preference': 'low', 
'relayed_by': '35.226.89.167', 
'received': '2023-07-05T08:53:48.287727164Z', 
'ver': 1, 
'double_spend': False,
'vin_sz': 1, 
'vout_sz': 2, 
'confirmations': 0, 
'inputs': [
    {'prev_hash': '79d841bf41ead0e4ecbb58197c289ec9cc087e85cf1a98196e2e415b8990357a',
     'output_index': 0, 
     'output_value': 100000,
     'sequence': 4294967295,
     'addresses': ['ltc1q7nyvlc6jkznpemw3g0n8f3z5z4eatfhevy07au'], 
     'script_type': 'pay-to-witness-pubkey-hash', 
     'age': 2502561,
     'witness': 
['3044022077515b45f26a56b0dfff42eb94b69d98dbf8fb896fda079ea7e99a17a768fd6f022008b3c435ee0816801e1eea22871cb935a7eaaa8df6ad472eab19b096fb62cd82'
, '034b3110d0be2b52a14c4bbccef285396c67c29586463f278a8d1efacb3c33f439']}], 
'outputs': [{
     'value': 10000, 
     'script': '00143358b02cabdf86e0fec7e0722e497285f568fcf4',
     'addresses': ['ltc1qxdvtqt9tm7rwplk8upezujtjsh6k3l85tw39ue'], 
     'script_type': 'pay-to-witness-pubkey-hash'}, 
     {'value': 88100, 
     'script': '0014f4c8cfe352b0a61cedd143e674c4541573d5a6f9', 
     'addresses': ['ltc1q7nyvlc6jkznpemw3g0n8f3z5z4eatfhevy07au'], 
     'script_type': 'pay-to-witness-pubkey-hash'}]},
'tosign': ['']}

First, I tried using the simple_spend method as shown below…

from blockcypher import simple_spend
simple_tx = simple_spend(api_key = API_KEY, from_privkey=priv_key_hex,
to_address="ltc1qxdvtqt9tm7rwplk8upezujtjsh6k3l85tw39ue", to_satoshis=10000, coin_symbol="ltc")
print('tx:', simple_tx)

… and this error was produced:

TX Error(s): Tx NOT Signed or Broadcast
Unable to find a transaction to spend for address LhYFhgm6iai5da8ADeoUjs2BnAPoPm74cm.
Not enough funds in 0 inputs to pay for 1 outputs, missing -10000.
Not enough funds after fees in 0 inputs to pay for 1 outputs, missing -11400.
Error validating generated transaction: Transaction missing input or output.
Traceback (most recent call last):
  File "main.py", line 33, in <module>
    simple_tx = simple_spend(api_key = API_KEY, from_privkey=priv_key_hex, to_address="ltc1qxdvtqt9tm7rwplk8upezujtjsh6k3l85tw39ue", to_satoshis=10000, coin_symbol="ltc")
  File "/home/runner/sendltc/venv/lib/python3.10/site-packages/blockcypher/api.py", line 1684, in simple_spend
    raise Exception('Build Unsigned TX Error')
Exception: Build Unsigned TX Error

This indicates that the private key I provided is automatically being formatted as a legacy address, where no funds for the input transaction exist because I funded the segwit derivative of the private key. I have since verified that this code will properly execute transactions when I fund the legacy derivative of the private key. But it does not work when I attempt to involve a segwit addresses as the sender or receiver.

Since I am unsure of how to ensure that the simple_spend method attempts a segwit transaction, I tried constructing it piece-by-piece.

Here’s the code for that:

from bitcoinlib.keys import Key
from blockcypher import create_unsigned_tx, make_tx_signatures, broadcast_signed_transaction

API_KEY = '<api_key>'

wif="<compressed_wif>"


priv_key_hex = Key(wif, network = 'litecoin').private_hex
pub_key_hex = Key(wif, network = 'litecoin').public_hex

sender = Key(priv_key_hex, network = 'litecoin').address(prefix='ltc', script_type="p2wpkh", encoding='bech32')
inputs = [{'address': f"{sender}"}]
outputs = [{'address': 'ltc1qxdvtqt9tm7rwplk8upezujtjsh6k3l85tw39ue', 'value': 10000}]

unsigned_tx = create_unsigned_tx(inputs=inputs, outputs=outputs, include_tosigntx=True, coin_symbol="ltc", api_key = API_KEY)
print(unsigned_tx)

privkey_list = [str(priv_key_hex)]
pubkey_list = [str(pub_key_hex)]

tx_signatures = make_tx_signatures(txs_to_sign=unsigned_tx['tosign'], privkey_list=privkey_list, pubkey_list=pubkey_list)
print('')
print(tx_signatures)

tx = broadcast_signed_transaction(unsigned_tx=unsigned_tx, signatures=tx_signatures, pubkeys=pubkey_list, coin_symbol="ltc", api_key = API_KEY)
print('')
print(tx)

So when I try to run this, the aforementioned error is returned, stating that the script could not be verified. My hunch is that it has something to do with attempting to broadcast a legacy transaction while I provided a segwit address. Upon viewing similar threads on here, it would seem that the signature is being malformed either because there is a problem with how I’m deriving my keys, or somehow I need to set a flag indicating a segwit transaction. This could lead to the root of the problem, but I could also be overlooking other issues.

Any advice, pointers, or answers would be greatly appreciated. Thank you for your time.