hyperlane-monorepo/solidity/interfaces/IInterchainGasPaymaster.sol

// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity >=0.6.11;

/**
 * @title IInterchainGasPaymaster
 * @notice Manages payments on a source chain to cover gas costs of relaying
 * messages to destination chains.
 */
interface IInterchainGasPaymaster {
    function payGasFor(
        address _outbox,
        uint256 _leafIndex,
        uint32 _destinationDomain
    ) external payable;
}