buildTransaction method for exchanging bsc token

Solidity Programming
#1

I am learning a bit more about Web3 and have created a small project in nodejs where I want to sell a BSC token for BNB. However, when I use the swapExactTokensForETHSupportingFeeOnTransferTokens function as seen below I get an error message that the buildTransaction method is missing.

  • Where can I get that and where do I define it? Should it go into the ABI?

Any help on this would really be much appreciated. I am missing something here and have been trying to find an answer for my question all over the internet but canā€™t find anything relevant.

Thanks a lot for any pointers,
Marcus

pancakeswap2_txn = contract.functions.swapExactTokensForETHSupportingFeeOnTransferTokens(
    500000000, 0,
    [spending_this_token,buying_this_token],
    your_wallet_address,
    deadline
).buildTransaction({
    'from': your_wallet_address,
//    'gasPrice': web3.toWei('20','gwei'),
    'gasPrice': Web3Client.utils.toWei('20','gwei'),
    'gasLimit': estimate,
    'nonce': nonce,
})

The error message I get per below:

TypeError: contract.functions.swapExactTokensForETHSupportingFeeOnTransferTokens(ā€¦).buildTransaction is not a function

#2

it seems that you are trying to send a transaction using web3 directly with a saved private key

you could try to look at a simple example on how to make a transaction and then to adapt.

from that error it seems that buildTransaction is not a function for the object returned by that previous call

#3

Thanks for your reply. Yes I have examples of other web3 transactions, I only included parts of the code as thats the only relevant part to the issue.

It seems like the buildTransaction method is standard and used in multiple different examples, but I just canā€™t get the method itself. Feels like Iā€™m 95% there and this is the one thing missing. Having spent hours and hours on trying to get it to work Iā€™m near my limit.

Thanks anyway.

#4

You may find some examples in other forum threads

1 Like
#5

Maybe this helps: https://morioh.com/p/d3ef8b16c770

1 Like
#6

Thanks, but donā€™t think so unfortunately as that requires ā€œMyContract.jsonā€ and I donā€™t have a contract file. Iā€™m just exchanging existing tokens back to BNB. Thanks for trying though. Seems like an ā€œimpossibleā€ task for some reason but should be so basic. Surprised noone has done it properly.

#7

it looks like you try to call a contract function there, with some parameters, it should be as any other contract function call