How to create a withdraw function - solidity

Question

I created a basic contract for crowdfunding. But cannot figure out how to create a withdraw function.
Withdraw function will transfer a campaign's collected funds to the campaign's owner. This is my full crowdfunding contract:
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.9;
contract CrowdFunding {
event testConditon(
uint256 deadline,
uint256 currentTimeInMs,
uint256 diff,
bool condition
);
struct Campaign {
address payable owner;
string title;
string description;
uint256 target;
uint256 deadline;
uint256 amountCollected;
string image;
address[] donators;
uint256[] donations;
}
mapping(uint256 => Campaign) public campaigns;
uint256 public numberOfCampaigns = 0;
function createCampaign(
address _owner,
string memory _title,
string memory _description,
uint256 _target,
uint256 _deadline,
string memory _image
) public returns (uint256) {
Campaign storage campaign = campaigns[numberOfCampaigns];
uint256 currentTimeInMs = block.timestamp * 1000;
emit testConditon(
_deadline,
currentTimeInMs,
_deadline - currentTimeInMs,
_deadline > currentTimeInMs
);
require(
_deadline > currentTimeInMs,
"The deadline must be in the future"
);
campaign.owner = payable(_owner);
campaign.title = _title;
campaign.description = _description;
campaign.target = _target;
campaign.deadline = _deadline;
campaign.image = _image;
campaign.amountCollected = 0;
numberOfCampaigns++;
return numberOfCampaigns - 1;
}
function donateToCampaign(uint256 _id) public payable {
uint256 amount = msg.value;
Campaign storage campaign = campaigns[_id];
campaign.donators.push(msg.sender);
campaign.donations.push(amount);
(bool sent, ) = payable(campaign.owner).call{value: amount}("");
if (sent) {
campaign.amountCollected += amount;
}
}
function getDonators(uint256 _id)
public
view
returns (address[] memory, uint256[] memory)
{
return (campaigns[_id].donators, campaigns[_id].donations);
}
function getCampaigns() public view returns (Campaign[] memory) {
Campaign[] memory allCampaigns = new Campaign[](numberOfCampaigns);
for (uint256 i = 0; i < numberOfCampaigns; i++) {
Campaign storage item = campaigns[i];
allCampaigns[i] = item;
}
return allCampaigns;
}
function withdraw(uint256 _id) public {
Campaign storage campaign = campaigns[_id];
require(
campaign.amountCollected >= campaign.target,
"The campaign has not reached its target"
);
//deadline has passed
// require(
// campaign.deadline < block.timestamp * 1000,
// "The deadline has not passed yet"
// );
require(
campaign.owner == msg.sender,
"Only the owner of the campaign can withdraw the funds"
);
campaign.owner.transfer(campaign.amountCollected);
campaign.amountCollected = 0;
}
}
I have no idea how to solve this issue.

Answer 1

Looks like you are missing the payable keyword to trigger the token transfer. Try this:
function withdraw(uint256 _id) public {
Campaign storage campaign = campaigns[_id];
(bool success, ) = payable(campaign.owner).call{value: campaign.amountCollected}("");
require(success, "Withdrawal failure");
campaign.amountCollected = 0;
}
Warning: this function and your function are having a reentrency vulnerability.