Estimating Gas Fees

function quote(
    uint32 _dstEid, // destination endpoint id
    bytes memory payload, // message payload being sent
    bytes memory _options, // your message execution options
    bool memory _payInLzToken // boolean for which token to return fee in
) public view returns (uint256 nativeFee, uint256 zroFee) {
    return _quote(_dstEid, payload, _options, _payInLzToken);
}

// How the _quote function works.
// This function is already defined in your OApp contract.
/// @dev the generic quote interface to interact with the LayerZero EndpointV2.quote()
function _quote(
    uint32 _dstEid,
    bytes memory _message,
    bytes memory _options,
    bool _payInLzToken
) internal view virtual returns (MessagingFee memory fee) {
    return
        endpoint.quote(
            MessagingParams(_dstEid, _getPeerOrRevert(_dstEid), _message, _options, _payInLzToken),
            address(this)
        );
}

// @dev Requests a nativeFee/lzTokenFee quote for sending the corresponding msg crosschain through the layerZero Endpoint
function quoteSend(
    SendParam calldata _sendParam, // send parameters struct
    bytes calldata _extraOptions, // extra message options
    bool _payInLzToken, // bool for payment in native gas or LzToken
    bytes calldata _composeMsg, // data for composed message
    bytes calldata _oftCmd // data for custom OFT behaviours
)
    public
    view
    virtual
    returns (
        MessagingFee memory msgFee, // fee struct for native or LzToken
        OFTLimit memory oftLimit,
        OFTReceipt memory oftReceipt,
        OFTFeeDetail[] memory oftFeeDetails // @dev unused in the default implementation, future proofs complex fees inside of an oft send
    )
{
    (oftLimit, oftReceipt) = quoteOFT(_sendParam);

    (bytes memory message, bytes memory options) = _buildMsgAndOptions(
        _sendParam,
        _extraOptions,
        _composeMsg,
        oftReceipt.amountCreditLD
    );

    msgFee = _quote(_sendParam.dstEid, message, options, _payInLzToken);
}