swapExactTokensForTokens failing

Question

Ive been reading other results but none of them fits my situation*

I cannot resolve this issue for a while. When im running this script:

• WBNB to DOGE - Works.
• DOGE to WBNB - Fails.

What am I doing wrong?

1. im registering the amountIn with (router.getAmountsOut())
2. im approving the token combination with the amountIn (Token.approve())

    const pair = [TOKENS.DOGE, TOKENS.WBNB]
    const amountIn = ethers.utils.parseUnits(val, 'ether')
    const amounts = await router.getAmountsOut(amountIn, pair);
    const amountOutMin = amounts[1].sub(amounts[1].div(15))

    const gasPrice = ethers.utils.parseUnits('5', 'gwei')
    const gasLimit = 2000000

    // Token = Token(TOKENS.DOGE)
    await Token.approve( pancakeRouter, amountIn, { gasLimit, gasPrice } )

    const buyTx = await router.swapExactTokensForTokens(
      amountIn,
      amountOutMin,
      pair,
      wallet.address,
      Math.floor(Date.now() / 1000) + 60 * 10,
      { gasLimit, gasPrice }
    )

Error:

  reason: 'transaction failed',
  code: 'CALL_EXCEPTION',
  transactionHash: '0xabd9862116711eacaa109d4a832c87e947af666745186b51cce7fe864a310c96',

Answer 1

Step 1:

Get the ABI of the token (contract), that is an interface of all available methods you can use of that token.

On bscscan you can signup for an api then you can query for the ABI of each token. Api url looks similar like: https://api.bscscan.com/api?module=contract&action=getabi&address=[TOKEN ADDRESS HERE]&apikey=[YOUR API KEY HERE] and store it to a var ABI or something.

// I use axios for HTTP get request
// Change [TOKENADDRESS] and [YOURAPIKEYHERE]

const ABI = await axios.get(`https://api.bscscan.com/api?module=contract&action=getabi&address=[TOKENADDRESS]&apikey=[YOURAPIKEYHERE]`);

Step 2:

Get the decimals of that contract, I do that in NodeJS:

var Contract = require('web3-eth-contract');

// This is the websocket url of a bsc node
Contract.setProvider('wss://bsc-ws-node.nariox.org:443');

var contractDecimals = new Contract(ABI, 'token address');
var decimals = await contractDecimals.methods.decimals().call();

Step 3: Prepare the value to approve of selling

// I use the ethers API here
const ethers = require('ethers');

// Get the balance of your wallet
// Change [YOUR WALLET ADDRESS HERE]
const balance = await contract.balanceOf([YOUR WALLET ADDRESS HERE]);

// approval with the decimals of the token
const valueToApprove = ethers.utils.parseUnits(balance.toString(), decimals);

Step 4: Approve the sell (You know how that works)

Step 5: Sell!

router.swapExactTokensForETHSupportingFeeOnTransferTokens(
        balance,
        0,
        [TokenToSellHere, [WBNBAddress HERE]],
        recipient, // Your wallet
        Math.floor(Date.now() / 1000) + 60 * 2, // 2 minutes from the current Unix time
        {
            gasPrice: ethers.utils.parseUnits(5', 'gwei'),
            gasLimit: 450000
        }

That's it!

Answer 2

Doge has 8 decimals. You need to specify it.

Also I think it is better to use a different method than router.swapExactTokensForTokens