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How do you calculate maxFeePerGas on Scroll and Mantle because they do not return maxFeePerGas and maxPriorityFeePerGas when fetching fee data?

founder www.joinclamp.com | @0xpolygon village and @hadronfc ‘24 | software engineer, web3 enthusiast, cheesecake connoisseur | deep diving into erc4337 

Following this one; I haven’t been able to use scroll reliably on testnet so far :(

DX Engineer | Head of Developer Relations at /pinata | Tinkering with everything | stevedylan.dev/links

Figured how to make it work on Scroll, Mantle not yet.

Started with the bare basics: 

maxFeePerGas = baseFeePerGas + maxPriorityFeePerGas

if we know the two right hand side variables then we can calculate maxFeePerGas.

But the network is live and blocks are being processed which means it’s the RPC that’s at fault. 

We decided to fetch baseFeePerGas from a different method. This was interesting

But the network is live and blocks are being processed which means it’s the RPC that’s at fault. 

We decided to fetch baseFeePerGas from a different method. This was interesting https://github.com/ethers-io/ethers.js/discussions/3601

“it simply multiplies the base fee by 2 and then adds the miner’s tip (maxPriorityFeePerGas)” 

Since the networks are actually working lastBaseFeePerGas cannot be null. Or unless the RPCs do not have a way to deconstruct the original equation and get the different values back.

So we decided to do it ourselves. We could parse this data directly and recreate the equation on our own and then submit it. 

Worked for Scroll at 1.5x. Failed for Mantle even at 2x which means we need a different equation and this won’t work.

Turns out Mantle doesn’t have support for 1559 yet. Hence, the problem. We should send legacy transactions with gasFee only.

The problem was since the RPC doesn’t return any value it’s difficult to even estimate baseFeePerGas which should be of the preceding block.