Send UserOp is failed when EIP-1559 is not supported

[alexkinno]

Describe the bug
Cannot send userOp to legacy network when used config with supports_eip1559 = false

To reproduce
Steps to reproduce the behavior:
Send the userOp to the bundler with network which doesn't support EIP-1559. Got an error:

2025-03-23T16:04:08.361813Z ERROR rundler_builder::bundle_sender: Failed to send bundle with unexpected error: RPC Error: server returned an error response: error code -32000: RPC error response: dynamicFee tx is not supported by signer

Expected behavior
It should be able to send UserOp to legacy network when supports_eip1559 = false is set

Logs
Please attach any relevant logs.

Additional context
Add any other context about the problem here.

[alexkinno]

@dancoombs Any ideas?

[dancoombs]

Hey @alexkinno, the correct flag for this is eip1559_enabled. Looks like we have an old flag in the arbitrum.toml file if if that is where you got the flag name from.

That being said, Rundler doesn't actually support legacy networks at the moment. The eip1559_enabled is only used to turn off priority fees on Arbitrum networks. We should rename the flag.

We're open for contributions if you'd like to to get it working on a legacy network. You'll need to (at a minimum):

1. Add a check in precheck.rs that ensures a UOs max_fee_per_gas == max_priority_fee_per_gas
2. Modify transaction creation in the builder to use gas_price instead of the 1559 fields. There may also be a few places where we assume 1559 transaction types.
3. Modify bundle fee estimation to estimate gas_price and set it equal to both max_fee_per_gas max_priority_fee_per_gas

Thats off the top of my head, there may be a few other required modifications missing.

[alexkinno]

@dancoombs Thank you for detailed response! We will check this out.