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I have been trying to swap two tokens using Uniswap Routers. I keep getting:

Error: Returned error: VM execution error.

I have checked my code many times, have no idea what the issue could be.

async function getValueAtAddress(host, deployedContractAbi, deployedContractAddress) { 
const amountIn = web3.utils.toWei('0.01');
const web31 = new web3(host);  
const jackycoin = new web31.eth.Contract(deployedContractAbi, deployedContractAddress);
const bal = await jackycoin.methods.balanceOf('0xE6082a3FfdceBd999a34c32FDb2630a9EeaeCe6A').call();
const weth = new web31.eth.Contract(wethABI, WETH_ADDRESS);
const router = new web31.eth.Contract(importedRouterABI.abi, ROUTER_ADDRESS);


await weth.methods.deposit().call(); //{value: amountIn}
await weth.methods.approve(ROUTER_ADDRESS, amountIn).call();

const amountsOut = await router.methods.getAmountsOut(amountIn, [WETH_ADDRESS, JACKYCOIN_ADDRESS]).call();
const amountOutMin = web3.utils.toBN(amountsOut[1])
    .mul(web3.utils.toBN(90))
    .div(web3.utils.toBN(100));

const balanceJackyCoinBefore = await jackycoin.methods.balanceOf('0xE6082a3FfdceBd999a34c32FDb2630a9EeaeCe6A').call();
const params = { 
  "amountIn": amountIn, 
  "amountOutMin": amountOutMin, 
  "path": [WETH_ADDRESS, JACKYCOIN_ADDRESS], 
  "to": '0xE6082a3FfdceBd999a34c32FDb2630a9EeaeCe6A',
  "deadline": Math.floor((Date.now() / 1000)) + 60 * 10
  // "value": BigNumber.from(0)
}

await router.methods.swapExactTokensForTokens(...Object.values(params)).call();


console.log("test6");

The full error trace:

Error: Returned error: VM execution error.
at Object.ErrorResponse (D:\OneDrive\Documents\Degree CS\Year 3\Individual Project\Website\TestingWeb\coursework\node_modules\web3-core-helpers\lib\errors.js:28:19)        
at D:\OneDrive\Documents\Degree CS\Year 3\Individual Project\Website\TestingWeb\coursework\node_modules\web3-core-requestmanager\lib\index.js:302:36
at XMLHttpRequest.request.onreadystatechange (D:\OneDrive\Documents\Degree CS\Year 3\Individual Project\Website\TestingWeb\coursework\node_modules\web3-providers-http\lib\index.js:98:13)
at XMLHttpRequestEventTarget.dispatchEvent (D:\OneDrive\Documents\Degree CS\Year 3\Individual Project\Website\TestingWeb\coursework\node_modules\xhr2-cookies\dist\xml-http-request-event-target.js:34:22)
at XMLHttpRequest._setReadyState (D:\OneDrive\Documents\Degree CS\Year 3\Individual Project\Website\TestingWeb\coursework\node_modules\xhr2-cookies\dist\xml-http-request.js:208:14)
at XMLHttpRequest._onHttpResponseEnd (D:\OneDrive\Documents\Degree CS\Year 3\Individual Project\Website\TestingWeb\coursework\node_modules\xhr2-cookies\dist\xml-http-request.js:318:14)
at IncomingMessage.<anonymous> (D:\OneDrive\Documents\Degree CS\Year 3\Individual Project\Website\TestingWeb\coursework\node_modules\xhr2-cookies\dist\xml-http-request.js:289:61)
at IncomingMessage.emit (node:events:402:35)
at endReadableNT (node:internal/streams/readable:1343:12)
at processTicksAndRejections (node:internal/process/task_queues:83:21) {
data: 'Reverted 0x08c379a0000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000245472616e7366657248656c7065723a205452414e534645525f46524f4d5f4641494c454400000000000000000000000000000000000000000000000000000000'

←[37;40mnpm←[0m ←[0m←[31;40mERR!←[0m ←[0m←[35mcode←[0m ELIFECYCLE ←[0m←[37;40mnpm←[0m ←[0m←[31;40mERR!←[0m ←[0m←[35merrno←[0m 1 ←[0m←[37;40mnpm←[0m ←[0m←[31;40mERR!←[0m←[35m←[0m [email protected] start:node app.js ←[0m←[37;40mnpm←[0m ←[0m←[31;40mERR!←[0m←[35m←[0m Exit status 1 ←[0m←[37;40mnpm←[0m ←[0m←[31;40mERR!←[0m←[35m←[0m ←[0m←[37;40mnpm←[0m ←[0m←[31;40mERR!←[0m←[35m←[0m Failed at the [email protected] start script. ←[0m←[37;40mnpm←[0m ←[0m←[31;40mERR!←[0m←[35m←[0m This is probably not a problem with npm. There is likely additional logging output above. ←[0m ←[37;40mnpm←[0m ←[0m←[31;40mERR!←[0m←[35m←[0m A complete log of this run can be found in: ←[0m←[37;40mnpm←[0m ←[0m←[31;40mERR!←[0m←[35m←[0m C:\Users\jacky\AppData\Roaming\npm-cache\_logs\2022-03-13T12_36_51_984Z-debug.log ←[0m

The tokens used have all been deployed to the Kovan network and work with no issues.Does anybody know what the issue might be?

1 Answer 1

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If you decode the string, it turns out to be "TransferHelper: TRANSFER_FROM_FAILED" which makes me think that you have not approved the router to spend your tokens. You need to approve the router before calling swap on it.

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  • thank you @Meet for the help. Don't the lines: await weth.methods.deposit().call(); //{value: amountIn} and await weth.methods.approve(ROUTER_ADDRESS, amountIn).call(); Approve the router address? Would you suggest anything different?
    – Btadford
    Mar 14, 2022 at 10:24
  • @Btadford it does actually, didn't notice that, in that case I'd try and make sure there's enough balance for the swap requested amount i.e. amountIn
    – Meet
    Mar 14, 2022 at 11:35
  • I fetch this from Uniswap so I'm pretty sure its correct, have also tried many different alternations of it. So I'm not sure that is the issue. I am running this in my server.js using VueJS. Would that cause any issues? @Meet
    – Btadford
    Mar 15, 2022 at 10:11
  • @Btadford check await weth.methods.balanceOf(signer_address).call() and see if it is greater than 10 ** 16 assuming toWei('0.02') takes input in eth units
    – Meet
    Mar 15, 2022 at 14:28

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