Smart Contract - BEP20: transfer amount exceeds allowance

Question

I'm new in solidity and I'm trying to swap tokens from "Address A" to "Address B".

I used the functions approve and transferFrom, but I'm still getting the error: "Error: VM Exception while processing transaction: reverted with reason string 'BEP20: transfer amount exceeds allowance'"

Could you please help me with this issue?

// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity ^0.8.3;

import "./CryptoPlinkoBall.sol";
import "./CryptoPlinko.sol";

import "hardhat/console.sol";

contract TokenSwap {
    address admin;
    address public owner;
    address private _token;

    constructor(address token) {
        admin = msg.sender;
        _token = token;
    }

    function swapTokens(address recipient, uint256 amount) external {
         BEP20(_token).approve(msg.sender, amount);
        BEP20(_token).allowance(msg.sender, address(this));
        BEP20(_token).transferFrom(msg.sender, recipient, amount);
    }

}

score 1 · Accepted Answer · answered Dec 02 '21 at 02:25

1

When you call BEP20(_token).approve(msg.sender, amount); you are approving the user to move that amount of tokens that the contract owns if you want to transfer the tokens from the user, the user should have called the token contract and approved the amount before calling this function, if you are doing the frontend that will interact with the contract you will need to put the call to the token contract first then the call to this contract

answered Dec 02 '21 at 02:25

jhonny

805
4
10

Hi jhonny, thank you very much! After your post I understood how the things should work. – Bruno Massaro Dec 03 '21 at 03:27

score 0 · Answer 2 · answered Dec 01 '21 at 13:35

0

The approve must be mined before the transferFrom gets called.You can't do both on the same call, meanning the approve should occur before going into the swapTokens function.

answered Dec 01 '21 at 13:35

Julissa DC

251
3
14

Smart Contract - BEP20: transfer amount exceeds allowance

2 Answers2