Stake function

pmknStake.sol

pragma solidity 0.8.4;

contract PmknFarm {

    function stake() public payable {
        require(
            msg.value > 0,
            "You cannot stake zero tokens"
        );
        if(isStaking[msg.sender] == true){
            uint256 toTransfer = calculateYieldTotal(msg.sender);
            pmknBalance[msg.sender] += toTransfer;
        }
        stakingBalance[msg.sender] += msg.value;
        startTime[msg.sender] = block.timestamp;
        isStaking[msg.sender] = true;
        emit Stake(msg.sender, msg.value);
    }

}