execution reverted: "ERC20: insufficient allowance" on transfer method (not transferFrom)

Question

I'm developing a Smart Contract that transfer tokens that are owned by the Smart Contract itself. The function to do that is pretty simple:

pragma solidity 0.8.1;
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
contract TransferTokens {
IERC20 token;

constructor(){
    token = IERC20(0x...);
}

function sendTokens(address receiver, uint256 amount) external {
    token.transfer(receiver, amount);
}

}

And I'm getting: execution reverted: ERC20: insufficient allowance

I have deployed my own token, which is an Openzeppelin ERC20 contract. That revocation happens in _spendAllowance function, which is invoked in transferFrom function, not in transfer function.

How can it be possible to get an error (from transferFrom function) that should not be thrown in my function (transfer function)?

How could I make my contract able to send the received ERC20 tokens, after a function execution?

it doesn't matter, you need to approve the receiver before transferring the token — Julissa DC, Jun 24 '22 at 14:01
I don't get your point: Who should approve the Smart Contract's address? The Smart Contract is trying to transfer its own tokens (on its balance). — Alexander Herranz, Jun 24 '22 at 14:45
Does this answer your question? How to programmatically detect and accept ETH and ERC20 deposits — Paul Razvan Berg, Jun 24 '22 at 18:50
No, sorry. I want to make my contract able to send the received ERC20 tokens, after a function execution. And I do not understand why I received an error from transferFrom function, when I using transfer function. — Alexander Herranz, Jun 26 '22 at 11:26
@AlexAcc The code supplied works as expected. It could be that you were using an old version that called transferFrom? Or you are using an ERC20 token that has a different implementation? — Ismael, Jun 28 '22 at 17:30

score 0 · Answer 1 · answered Jun 26 '22 at 14:06

0

Have you checked balanceOf() with address of smart contract? Does it show any balance? Also, I don't understand why are you writing

IERC20 token = IERC20(tokenAddress);

You have already instantiatiated token in constructor. And what 'tokenAddress' are you passing?

answered Jun 26 '22 at 14:06

Ashish kumar

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Yes sure, the contract had the received balance. And you are right, that line of code was redundant, already instantiated. – Alexander Herranz Jun 26 '22 at 18:55

execution reverted: "ERC20: insufficient allowance" on transfer method (not transferFrom)

1 Answers1