[General] Failed transaction on ERC20 token transfer with paymaster.

[mshojaei-txfusion]

Environment

Mainnet

Provide a brief description of the functionality you're trying to implement.

We deployed an approval-based paymaster, and since then it managed to handle more than 800 transactions, but one specific user when tried to transfer some ZKUSD tokens, the transaction failed, we also tried to reproduce the error but we successfully managed to do the same transaction.

What is the specific issue or error you're encountering?

• ERC20 Token is transferred to the paymaster contract
• Transaction was erc20 token transfer of ZKUSD
• Transaction is failed with this error Error function_selector = 0x, data = 0x

Can you share the error messages or logs you're receiving, if any?

This is the transaction address: https://explorer.zksync.io/tx/0x37eb2a44bd3c71a5a42d3a89adc9500dbda4e2a512e0286c9fdec3455d1f469c

Status: Failed
Reason: Error function_selector = 0x, data = 0x

Have you made any recent changes to the contract before encountering this issue?

Not at all.
all clients and smart contracts are the same as before (when the other 800 transactions with Paymaster succeed).

Are there any external libraries or contracts that your contract interacts with?

The user tried to transfer the ERC20 token and also used Paymaster.
ERC20 Token Contract: https://explorer.zksync.io/address/0xfC7E56298657B002b3e656400E746b7212912757
Paymaster address: https://explorer.zksync.io/address/0x5F0B9f4f6BaB83521170A9C82610A9F006625B6F

Can you provide the relevant portions of your contract code where the issue is occurring?

we believe that the problem is not related to the paymaster, but also do not have any idea why this happened.
anyway our paymaster is similar to this paymaster example (but not fixed price, connected to a price feed): https://github.com/matter-labs/paymaster-examples/blob/main/contracts/contracts/paymasters/ERC20fixedPaymaster.solhappened

Have you tried to isolate the problem, and if so, what were the results?

No, could not even reproduce the problem, but successfully managed to transfer ZKUSD with the same paymaster:
https://explorer.zksync.io/tx/0xd45c13a309aac609052ea30a93a300e9b771baa55aa7cf82934237e07e9621b0

What steps have you already taken to try to resolve the issue?

Before there was a similar problem that randomly failing transactions with Paymaster, the ML team said the reason behind it was sometimes transactions did have not enough gas fees that other transactions could cover their lack of gas fees, so they said the problem was with estimation, and then the problem was fixed by topping up the estimations.
but in this case, if you check the transaction link I sent you can see that a good amount of the transaction fee is refunded.
so the problem can not be having enough transaction fees.

Repo Link (Optional)

portal.txsync.io

Additional Details

No response

[ZKBitcoinToken]

I have been submitting tons of answers to my paymaster and I get failed transactions all the time on it. It happens when two concurrent answers are submitted that are both valid at the time, but once one is accepted the other becomes invalid. This invalid transaction will still go to the paymaster and FAIL and make the paymaster pay fee. I think this is a big error

[ZKBitcoinToken]

https://goerli.explorer.zksync.io/tx/0xa8b62ec56ae1346fe93ed49d2ba0437c5eb1a491c9473d0d29ac5bdba08ddf89
https://goerli.explorer.zksync.io/tx/0xa9715d333b7075ab7cb5aa6f493ce709e92f5ecbfd4aaf917b1b750349a30911
https://goerli.explorer.zksync.io/tx/0xb2333ea661f7376086a6f145adfef3b7317ff662cb32b8d47ec252e14a8d18c2
https://goerli.explorer.zksync.io/tx/0xa9715d333b7075ab7cb5aa6f493ce709e92f5ecbfd4aaf917b1b750349a30911

Failed transactions PAID BY PayMaster
I can recreate easily

[MexicanAce]

It happens when two concurrent answers are submitted that are both valid at the time, but once one is accepted the other becomes invalid [...]

@ZKBitcoinToken can you expand what you mean by "two concurrent answers"? If you have steps for recreating this issue, would you please post them in this thread for us to dig in further?

[ZKBitcoinToken]

Sorry was wrong about this, my PayMaster wasnt checking things correctly,

[MexicanAce]

anyway our paymaster is similar to this paymaster example

@mshojaei-txfusion Could you please post the code for the paymaster so we can take a closer look? The error Error function_selector = 0x, data = 0x can be generic at times, but usually refers to accessing methods that don't exist.

[MexicanAce]

It's also possible to investigate further using the era_test_node tool to replay the transaction locally for further details: https://era.zksync.io/docs/tools/testing/era-test-node.html#replay-remote-transactions-locally

[ZKBitcoinToken]

It happens when two concurrent answers are submitted that are both valid at the time, but once one is accepted the other becomes invalid [...]

@ZKBitcoinToken can you expand what you mean by "two concurrent answers"? If you have steps for recreating this issue, would you please post them in this thread for us to dig in further?
I actually was mistaken, I think we need to add a

I think I am mistaken and we need a

    require(gasleft() > GAS_BUFFER2, "Not enough gas left to safely proceed, please raise your gasLimit before sending");

But his error doesnt seem related to out of gas? So I am not sure, it doesnt seem like there was any error in the transfer (the user had that amount of USDC, maybe the transfer attempted to move too much UDSC or other asset he didnt have causing it to error??