"Max" button causes transaction revert on Base (USDC to ETH swap)

[Buidlor]

Bug Report: "Max" button causes transaction revert on Base (USDC to ETH swap)

Date: 2026-02-07
Widget: RelayKit SwapWidget (@relayprotocol/relay-kit-ui)

What happened

• User has 5.19619 USDC on Base
• Pressed "Max" in the swap widget to swap USDC to ETH
• Transaction was submitted but reverted on-chain
• Reducing input to 5.19 USDC (slightly below max) -> transaction succeeds immediately

On-chain evidence

• Reverted tx: https://basescan.org/tx/0x9919e198a4b19c659f656ec825d6ce965c65955910f7deccc350f83f894e5a24
• Method: transferAndMulticall on RelayApprovalProxyV3
• Gas used: 523,950 / 530,250 (98.8%)
• No revert reason exposed
• The user paid gas fees for a failed transaction

Expected behavior

The "Max" button should leave a small dust buffer or the solver should handle the full-balance edge case so the swap doesn't revert.

Environment

• Chain: Base (8453)
• Swap: USDC to ETH
• Wallet: Privy embedded wallet (confirmation modals disabled)
• Gas sponsorship: not enabled

SDK versions

• @relayprotocol/relay-kit-ui: ^7.0.4
• @relayprotocol/relay-kit-hooks: ^3.0.1
• @relayprotocol/relay-sdk: ^4.0.1
• @relayprotocol/relay-svm-wallet-adapter: ^15.0.1
• @privy-io/react-auth: ^3.11.0
• @privy-io/wagmi: ^2.0.2
• viem: ^2.40.2
• wagmi: ^2.19.4

[pedromcunha]

We're going to patch this, right now we only add a buffer on ETH max swaps. I'll let you know when we push a fix

[Buidlor]

Thank you @pedromcunha ,
Appreciating the follow up