Add gas and refunds

Add gas

If the gas you paid isn't enough, for example because the destination gas price rose, the message waits on Axelarscan with an Insufficient fee status. Add gas to it on the source chain, and it continues.

The easiest way is the Add gas button on the message's Axelarscan page, or the AxelarJS SDK. See Recover a message.

To do it from a contract or script, call the gas service on the source chain. The message is identified by the hash of the transaction that sent it and the index of its ContractCall event log in that transaction:

function addNativeGas(
    bytes32 txHash,
    uint256 logIndex,
    address refundAddress
) external payable;

The ERC-20 variants take a gasToken and gasFeeAmount, and need an approval first. Gas you add that isn't used is refunded like the rest.

Refunds

Gas left after execution is refunded on the source chain to the refund address you set when paying gas (how refunds are calculated). Refunds are sent in the token you paid with, except on XRPL, where they're in XRP.

The refund address is the last argument of every payment function:

gasService.payNativeGasForContractCall{ value: msg.value }(
    address(this),
    destinationChain,
    destinationAddress,
    payload,
    msg.sender // refund address
);

msg.sender refunds the user who called your contract. To refund somewhere else, pass that address instead, or let the caller choose by taking it as a parameter. If you pass address(this), your contract receives the refund, so it needs a way to receive native tokens (a receive function) and to withdraw them.

Each refund emits a Refunded event on the gas service, and appears on the message's Axelarscan page.