Underestimation of fee

[Carryme1899]

Ethers Version

5.6.6

Describe the Problem

I'm trying to send a transaction on Polygon Mumbai testnet.

It seems that Ethers had a wrong estimate(too low) in maxPriorityFeePerGas and maxFeePerGas, so my transaction stuck in mempool and finally got dropped.

When I use metamask and same RPC endpoint to transfer, the transaction was successfully confirmed.

Code Snippet

const provider = new ethers.providers.JsonRpcProvider(
  `${ALCHEMY_ENDPOINT}${API_KEY}`
);
const wallet = ethers.Wallet
  .fromMnemonic(SIGNER_MNEMONIC)
  .connect(provider);

let tx: TransactionRequest = {
  to: toAddress,
  value: parseUnits(value, "ether"),
};

let p = await wallet.populateTransaction(tx);
// p.maxFeePerGas:  { "type": "BigNumber", "hex": "0x59682f12" }
// p.maxPriorityFeePerGas:  { "type": "BigNumber", "hex": "0x59682f00" }
// Too low?

Update

So I tried to set gas fee by myself but the transaction still failed.
Did I do something wrong?

let tx: TransactionRequest = {
  to: toAddress,
  value: parseUnits(value, "ether"),
  maxFeePerGas: parseUnits("150", "gwei"),
  maxPriorityFeePerGas: parseUnits("100", "gwei")
};

Update 2

I found that the error might be caused by an incorrect nonce.
Ethers use getTransactionCount("pending") as the transaction nonce, but that is not the correct number for my account.

So I change the code:

const nonce = BigNumber.from(await wallet.getTransactionCount("latest"));

let tx: TransactionRequest = {
  to: toAddress,
  value: parseUnits(value, "ether"),
  nonce: nonce
};

and it works as expected!

[zemse]

The provider tries with provider.getFeeData() if the node gives any fee data.

For polygon mumbai:

> await p.getFeeData()
{
  maxFeePerGas: BigNumber { value: "1500000014", hex: "0x59682f0e" }, // 1.500000014
  maxPriorityFeePerGas: BigNumber { value: "1500000000", hex: "0x59682f00" }, // 1.5
  gasPrice: BigNumber { value: "38817777780", hex: "0x0909b84874" } // 38.81777778
}

By default, ethers will use EIP1559, and hence use maxFeePerGas and maxPriorityFeePerGas provided by the node. But seems this is incorrect. If you want ethers to use the non-EIP1559 gasPrice i.e. 38 gwei, then you can specify that in this way:

await wallet.populateTransaction({...tx, type: 0}); // does not use EIP1559

[zemse]

On a separate note, EIP1559 networks ideally should have baseFee to be varing much based on congestion and priority fee to stay pretty constant. However, on matic mainnet, I've mostly observed baseFee to be very less and priority fee to be huge and varying much. So I don't think the benefits of EIP1559 are much realized there. Maybe that's because most of the transactions are not type:2 (not sure if this is accurate, just a guess).

[ricmoo]

The polygon network uses a non-standard implementation of EIP-1559 and the algorithms they choose don’t provide the economic incentives that it was designed around.

As a result, the maxPriorityFeePerGas must be set incredibly high (last I tried, 35 gwei), but they basically use the maxPriorityFeePerGas as an analog for legacy gasPrices.

As a result, there is no reliable way to automatically provide meaningful bounds on transaction times, like EIP-1559 provides, and to use it reliably you must use a gas station oracle, similar to legacy Ethereum transactions. There do exist polygon gas station oracles though; if anyone would like to post links in this issue to the ones they use, that might help others trying to use the polygon networks.