Ethereum Swap Exact Tokens For Tokens Error: TRANSFER_FROM_FAILED Even After Approval
As a Ethereum user, you’re likely familiar with the popular Uniswap V2 protocol, which allows for the swapping of two types of tokens (ExactTokens and any other token) without the need to transfer one of them from your wallet. However, sometimes errors occur that prevent this swapping process, including the infamous «Transfer From Failed» error after approval.
In this article, we’ll delve into the possible causes behind this error and explore ways to resolve it.
What is SwapExactTokensForTokens?
SwapExactTokensForTokens is a Ethereum protocol used for token swaps. It’s similar to Uniswap V2, but instead of swapping two tokens, it allows you to swap one ExactToken (ETX) with one or more other tokens (TX). This can be beneficial when using the ETX as collateral in lending mechanisms.
Why does SwapExactTokensForTokens error occur?
The «Transfer From Failed» error typically occurs when the following conditions are met:
- The user has approved the swap contract.
- You have a sufficient balance of ExactToken to transfer.
- You’re attempting to withdraw ETX from your wallet (even if it’s not your primary wallet).
If any one of these conditions is not met, the swap will fail.
Possible solutions
To resolve the «Transfer From Failed» error, try the following:
1. Check if you have approved the swap contract
Make sure you’ve successfully approved the SwapExactTokensForTokens contract using the swapExactTokensForTokens function on your local node.
pragma solidity ^0.8.0;
contract MySwapContract {
function swapExactTokensForTokens(address _to, uint256 amountIn, address[] memory _tokens, uint256 deadline) public override {
// approval logic here...
}
}
2. Verify your balance of ExactToken
Ensure that you have sufficient ETX to transfer in the first place.
pragma solidity ^0.8.0;
contract MySwapContract {
mapping(address => uint256) public etxBalances;
function getBalance(address _user) public view returns (uint256) {
return etxBalances[_user];
}
}
3. Check if your ETX is being sent to the swap contract
Verify that your ETX is indeed being transferred from your wallet to the SwapExactTokensForTokens contract.
pragma solidity ^0.8.0;
contract MySwapContract {
mapping(address => uint256) public etxBalances;
mapping(address => address) public txsSent;
function transferETX(address _user, address _to, uint256 amountIn) public payable {
// add logic here...
}
}
4. Wait for the «Transfer From Failed» error to be resolved
If you’re still experiencing issues, try waiting for a few hours and see if the problem resolves itself.
Conclusion
The «Transfer From Failed» error can occur due to various reasons, including insufficient balances or approvals on your local node. By verifying your ETX balance, checking approval logic, and ensuring that ETX is being sent to the swap contract, you should be able to resolve this issue. If the problem persists, it’s recommended to wait for a few hours before attempting to swap again.
Additional Resources
For more information on Ethereum protocol usage and troubleshooting, refer to:
- [Ethereum.org](
- [Uniswap V2 documentation](