Airdrop contract - Contract can't send token - ERC20 transfer amount exceeds allowance

Question

I am trying to create a contract which will be used as an airdrop contract. I will send tokens from a contract already deployed to it, and then any user can claim tokens to this airdrop contract. However I got an error : ERC20 transfer amount exceeds allowance. I am using transferFrom for this, I tried to increase allowance of the airdrop contract address, to approve .. like I saw in other posts, but still doesn't work. With the function transfer, I got an other error : solidity safemath subtraction overflow.

Do you have any idea what I am doing wrong ?

airdrop.sol 

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.0;

abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);


    constructor() {
        _transferOwnership(_msgSender());
    }

   
    function owner() public view virtual returns (address) {
        return _owner;
    }

    
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

   
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(address(0));
    }

   
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _transferOwnership(newOwner);
    }

   
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }

  
}

interface token{
     function transfer(address recipient, uint256 amount) external returns (bool);

     function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
}

contract airTortuga is Ownable{

      mapping (address=>bool)claimed;
      mapping (address=>bool) _blacklistedaddress;
      uint public amountToken=110000*10**9;
      uint public _airdropDelivered = 0;
      bool public airdropAlive = false;
      
      token _token;
      address[]  _blacklistedaddresses=[...];
      
      function setclaimtokenaddress(address add)public onlyOwner{
          _token=token(add);
      }
      function settokenamounttobeclaimed(uint amount)public onlyOwner{
          amountToken=amount*10**9;
      }
      function removeblackListAddress(address add)public onlyOwner{
           _blacklistedaddress[add]=false;
      }
      function resetairdropnumber()public onlyOwner{
          _airdropDelivered = 0;
      }
      function enableAirdropAlive()public onlyOwner{
          airdropAlive = true;
      }
      function disableAirdropAlive()public onlyOwner{
          airdropAlive = false;
      }
      
      function  blackListAddress()public onlyOwner{
          for (uint i; i<=_blacklistedaddresses.length-1; i++){
          _blacklistedaddress[_blacklistedaddresses[i]]=true;
          }
      }

      function claim()public{
          require(_blacklistedaddress[msg.sender]==false,'cant claim address blacklisted ');
          require(claimed[msg.sender]==false,'already claimed');
          require(airdropAlive==true,'no airdrop alive');
          
          _token.transferFrom(address(this), msg.sender, amountToken );
          _airdropDelivered = _airdropDelivered + 1;
          
          claimed[msg.sender]=true;
      }
    
}

score 0 · Answer 1 · answered Jan 10 '22 at 19:42

Change the line

_token.transferFrom(address(this), msg.sender, amountToken );

to

_token.transfer( msg.sender, amountToken );

Since you are calling the function from the smart contract, the sender is implicity the contract itself.

If you want to use .transferFrom() you have to first approve the transaction with .approve()

Airdrop contract - Contract can't send token - ERC20 transfer amount exceeds allowance

1 Answers1