function addBeneficiary(
        address beneficiary,
        uint256 startTime,
        uint256 releaseTime,
        uint256 amount
    )
        external
        onlyOwner
    {
        Info storage info = _info[beneficiary];
        require(!info.known, "This address is already known to the contract.");
        require(releaseTime > startTime, "Release time must be later than the start time.");
        require(releaseTime > block.timestamp, "End of vesting period must be somewhere in the future.");

        info.startTime = startTime; 
        info.totalAmount = amount; 
        info.releaseTime = releaseTime; 
        info.known = true; 
    }