Having errors with my "Withdraw" function in Solidity - solidity

Question

pragma solidity ^0.8.0;
//using safe math
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/math/SafeMath.sol";
import "hardhat/console.sol";
contract TimeLock {
/*
Functions to implement
//deposit
//withdraw
//increase timelock
//view time left
*/
/*
need to store balance per user and time per user
*/
using SafeMath for uint;
mapping(address => uint) public balancePerUser;
mapping(address => uint) public timeLeftPerUser;
function deposit( uint amount) external payable {
if(balancePerUser[msg.sender] == 0)
{
balancePerUser[msg.sender] = balancePerUser[msg.sender].add(amount);
timeLeftPerUser[msg.sender] = timeLeftPerUser[msg.sender] + block.timestamp + 8 seconds;
}
else {
balancePerUser[msg.sender] = balancePerUser[msg.sender].add(amount);
timeLeftPerUser[msg.sender] = timeLeftPerUser[msg.sender] + 8 seconds;
}
}
function increaseTimeLock( uint timeInSeconds) public {
timeLeftPerUser[msg.sender] = timeLeftPerUser[msg.sender].add(timeInSeconds);
}
function viewTimeLeft() public view returns (uint256) {
return timeLeftPerUser[msg.sender].sub(block.timestamp);
}
function checkBalance() public view returns (uint) {
return balancePerUser[msg.sender];
}
function withdraw() public payable {
// check that the sender has ether deposited in this contract in the mapping and the balance is >0
require(balancePerUser[msg.sender] > 0, "insufficient funds");
require(block.timestamp > timeLeftPerUser[msg.sender], "lock time has not expired");
// update the balance
uint amount = balancePerUser[msg.sender];
balancePerUser[msg.sender] = 0;
// send the ether back to the sender
payable(msg.sender).transfer(amount);
}
}
I initally deposit some money using the deposit function but upon using the withdraw function I get the following error. Can
The transaction has been reverted to the initial state.
Note: The called function should be payable if you send value and the value you send should be less than your current balance.
Debug the transaction to get more information.
Would appreciate any help with the same. Thanks!