How can I swap with the pair BUSD instead of BNB?

[rafaelfaria]

So, I have been building a bot, and so far, I have been successfully trading in BNB.

For the swap, I have been doing:

async function swap() {
       .
       .
       .

      const tx = await routerContract.swapExactETHForTokens(
        amountOutMin,
        [inputTokenAdress, tokenToBuyAddress],
        myWalletAddress,
        Date.now() + 1000 * 60 * 10, //10 minutes
        {
          gasPrice,
          gasLimit,
          value : amountIn,
          nonce
      });

      return await tx.wait();

}

Where inputTokenAdress is BNB address.

The problem is, when i try to use BUSD address 0xe9e7cea3dedca5984780bafc599bd69add087d56 the same transaction does not work.

I am getting

cannot estimate gas; transaction may fail or may require manual gas limit (error={"code":3,"response":"{\"jsonrpc\":\"2.0\",\"id\":6,\"error\":{\"code\":3,\"message\":\"execution reverted: PancakeLibrary: IDENTICAL_ADDRESSES\",\"data\":\"0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000002350616e63616b654c6962726172793a204944454e544943414c5f4144445245535345530000000000000000000000000000000000000000000000000000000000\"}}\n"}, method="call", transaction={"from":"0x0E216C385c647157671Fea70d36c0219BFaE553E","to":"0x10ED43C718714eb63d5aA57B78B54704E256024E","data":"0xd06ca61f0000000000000000000000000000000000000000000000001bc16d674ec8000000000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000000000000000000000000000000000000002000000000000000000000000bb4cdb9cbd36b01bd1cbaebf2de08d9173bc095c000000000000000000000000bb4cdb9cbd36b01bd1cbaebf2de08d9173bc095c","accessList":null}, code=UNPREDICTABLE_GAS_LIMIT, version=providers/5.5.0)

So the first thing I tried was to use swapExactTokensForTokens instead of swapExactETHForTokens

  tx = await this.routerContract.swapExactTokensForTokens(
          amountIn,
          amountOutMin,
          [inputTokenAdress, tokenToBuyAddress],
          myWalletAddress,
          Date.now() + 1000 * 60 * 10, //10 minutes
          {
            gasPrice,
            gasLimit
            nonce
        });

Then i get

replacement fee too low (error={"code":-32000,"response":"{\"jsonrpc\":\"2.0\",\"id\":153,\"error\":{\"code\":-32000,\"message\":\"replacement transaction underpriced\"}}\n"}, method="sendTransaction", transaction="0xf9016e82037085012a05f200830334509410ed43c718714eb63d5aa57b78b54704e256024e80b9010438ed17390000000000000000000000000000000000000000000000000de0b6b3a7640000000000000000000000000000000000000000000000000000000668f082ba709900000000000000000000000000000000000000000000000000000000000000a00000000000000000000000000e216c385c647157671fea70d36c0219bfae553e0000000000000000000000000000000000000000000000000000017ddccceaeb0000000000000000000000000000000000000000000000000000000000000002000000000000000000000000e9e7cea3dedca5984780bafc599bd69add087d56000000000000000000000000bb4cdb9cbd36b01bd1cbaebf2de08d9173bc095c8193a0fd0288921827db12053db38496e0c145963add24f26e80262919593f54fac035a00d44f97ab114656cc39c1496554c0d4973b94d6d02fba05e1a7f89cac8f78691", code=REPLACEMENT_UNDERPRICED, version=providers/5.5.0)```

According to [this](https://github.com/ethers-io/ethers.js/discussions/1745) topic, the problem is the nonce, that is saying that is trying to replace the previous transaction. But as the same as the author, I'm only putting one transaction at a time, and I am always calling

const nonce = await provider.getTransactionCount(myWalletAddress, 'latest');

Does anyone know what is happening?

[htadashi]

I think what is happening is that nonce is getting the total number of transactions mined, but you are not getting the lastest pending transaction. This answer on StackOverflow may help you.

[rafaelfaria]

Thanks, @htadashi ,

that StackOverflow answer makes sense.
I fixed it by removing the nounce i was passing through, but to be honest, not sure what is the impact of doing so.

Any ideas what happens if i don't pass the nounce?

[htadashi]

@rafaelfaria

AFAIK the default value should be equal to await provider.getTransactionCount(myWalletAddress, 'pending') :

ethers.js/packages/abstract-signer/src.ts/index.ts

Line 293 in eb432aa

if (tx.nonce == null) { tx.nonce = this.getTransactionCount("pending"); }

[rafaelfaria]

@htadashi awesome. Good to know. Thanks.

[rafaelfaria]

I wonder why when I use swapExactETHForTokens the nonce using provider.getTransactionCount(myWalletAddress, 'latest') works, however, when I am using swapExactTokensForTokens it doesn't.