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Fail with error 'TransferHelper: TRANSFER_ FROM_ FAILED'

2022-02-03 23:23:18 Q & A of Denglian community

test dai exchange eth When , Encounters an error Fail with error 'TransferHelper: TRANSFER_FROM_FAILED' Use uniswapV2Router.swapExactTokensForETH stay swap Before , Authorization has been made require(dai.approve(address(uniswapV2Router), amountIn), 'approve failed.') Why do you report such errors ?

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