Yesterday I sent out a transaction by manually specifying a very low max gas price on Metamask. Then I regretted doing that because my transaction stuck for hours.

So I tried to increase the gas price but I kept getting this “replacement transaction underpriced” error.

Later I found out the problem was that I need to increase the “priority fee” as well. Simply increasing max gas price is not enough.

Another interesting finding when I was trying to directly interact with the contract on Etherscan (although failed with the same error) is that 0x0 and 0x are different values for bytes fields. If you want to pass in empty value for the bytes type parameter, you should input 0x instead of 0x0.