INSUFFICIENT_OUTPUT_AMOUNT error when attempting Uniswap swap from a contract

Question

While I'm able to successfully swap ETH for DAI, I'm running into an INSUFFICIENT_OUTPUT_AMOUNT error when trying to swap DAI for ETH using swapExactTokensForETH, even with amountOutMin set to 0. I also tried with LINK with the same result: ETH => LINK works fine, LINK => ETH gives INSUFFICIENT_OUTPUT_AMOUNT.

I've tried both on Kovan and using Hardhat's forked mainnet. This is the function I'm trying to call:

  function swapTokensForEth(address token, uint amountIn, uint deadline) external payable {
    IERC20(token).transferFrom(msg.sender, address(this), amountIn);

    address[] memory path = new address[](2);
    path[0] = token;
    path[1] = uniswap.WETH();

    IERC20(token).approve(address(uniswap), amountIn);

    // https://uniswap.org/docs/v2/smart-contracts/library/#getamountout
    uint[] memory amountOutMin = getEstimatedTokenForETH(amountIn, path); // Fails even when this is 0.

    // https://uniswap.org/docs/v2/smart-contracts/router02/#swapexacttokensforeth
    uniswap.swapExactTokensForETH(
      amountIn,
      amountOutMin[1],
      path,
      msg.sender,
      deadline
    );
  }

  function getEstimatedTokenForETH(uint amountIn , address[] memory path) public view returns (uint[] memory) {
      return uniswap.getAmountsOut(amountIn, path);
  }

Answer 1

The input amounts I was using were too small.