How to create a raw ERC-4337 UserOperation's PaymasterAndData field from scratch and then send it to bundler?

Question

I am using Stackup's bundler to send my user operations.

I want to have my own Paymaster to let the user pay in ERC20 tokens. I cloned Pimlico's ERC20 Paymaster contract and deployed it. Now the issue I am facing is that I am not able to generate the correct paymasterAndData field.

If I use pimlico's SDK to generate the data, it returns something like this 0x848efc3d7d7b01d03c9885647de70b59677a73f1000000000000000000000000000000000000000000000000000000000000061f

And this is what they do internally to generate it

 const tokenAmount = await this.calculateTokenAmount(userOp)
        const paymasterAndData = utils.hexlify(
            utils.concat([this.contract.address, utils.hexZeroPad(utils.hexlify(tokenAmount), 32)])
        )
        return paymasterAndData

But when I send this user operation the bundler returns with code: -32500 - transaction rejected by entryPoint’s simulateValidation, during wallet creation or validation

But if I use pimlico's bundler and I use the pm_sponsorUserOperation rpc call, I get back this string 0x03b9a376b6bfda6fce215614b5be52b10528df3e0000000000000000000000000000000000000000000000000000000064e9d41c0000000000000000000000000000000000000000000000000000000000000000d5d89c31fbc2c692d9d85ba1eaa737470b97944256e61f06cb7c6f0f07c180d42f101d3d03ccf2cc6958652d915fe904adf15627ee505a7f1cb6a1dd2eac40f71b And this string is accepted by Pimlico's bundler as valid paymasterAndData, but won't work if I set this as the paymasterAndData field and send to stackup's bundler.

How do I generate a paymasterAndData field just by using pure ethers.js and not depend on the bundler to do it for me?

Answer 1

I have also created a userOp with Paymaster, but I have used the Biconomy SDK for it. I have created paymasterAndData using this. paymasterAndData: hexConcat([ paymaster.address, hexZeroPad(token.address, 20), ])

I hope this helps