PancakeSwap – Troubleshooting Nethereum Execution Reverted Errors on Binance Smart Chain

Jesus christ, I finally managed to make it work, HUGE thanks to @tqdpham96 for pointing out to root cause... I believe I wouldn't be able to find this somewhere else as there is absolutely NO information, and no one is talking that you should APPROVE coin for swap before doing actual swap.

So, basically, in details - before doing any swap, you make one-time approval for coin to swap from, you have to call approve() function on that coin. For example, if you're willing to swap from WBNB to CAKE then you have to approve WBNB, so that PancakeSwap would be able (had permission) to withdraw your WBNB in order to do swap for CAKE. And vice-verse, if you're willing to do swap from CAKE to WBNB, then you have to do everything the same - approve for CAKE, so that PancakeSwap had permission to withdraw your CAKE and deposit WBNB.

Here is FULLY working code on PancakeSwapV2Router for C#, which does approve() for initial coin (WBNB), and then does swap WBNB to CAKE, just provide private key and you are ready to go:

using Nethereum.Contracts;
using Nethereum.Hex.HexTypes;
using Nethereum.RPC.Eth.DTOs;
using Nethereum.Web3;
using Nethereum.Web3.Accounts;

using System;
using System.Numerics;
using System.Threading.Tasks;

class PancakeSwapExample
{
    // ready-to-run code
    static async Task Main(string[] args)
    {
        var yourWalletPrivateKey = "YOUR_WALLET_PRIVATE_KEY"; // Only this needs to be changed

        var pancakeSwapRouterV2AddressMainnet = "0x10ED43C718714eb63d5aA57B78B54704E256024E";
        var wbnbAddress = "0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c";
        var cakeAddress = "0x0E09FaBB73Bd3Ade0a17ECC321fD13a19e81cE82";
        var binanceTestnetNode = "https://bsc-dataseed.binance.org/";
        var binanceChainId = 56;
        var amount = 0.0002M; // amount in coins to swap

        var pancakeSwapRouterV2Abi =
            @"[{""inputs"":[{""internalType"":""address"",""name"":""_factory"",""type"":""address""},{""internalType"":""address"",""name"":""_WETH"",""type"":""address""}],""stateMutability"":""nonpayable"",""type"":""constructor""},{""inputs"":[],""name"":""WETH"",""outputs"":[{""internalType"":""address"",""name"":"""",""type"":""address""}],""stateMutability"":""view"",""type"":""function""},{""inputs"":[{""internalType"":""address"",""name"":""tokenA"",""type"":""address""},{""internalType"":""address"",""name"":""tokenB"",""type"":""address""},{""internalType"":""uint256"",""name"":""amountADesired"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountBDesired"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountAMin"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountBMin"",""type"":""uint256""},{""internalType"":""address"",""name"":""to"",""type"":""address""},{""internalType"":""uint256"",""name"":""deadline"",""type"":""uint256""}],""name"":""addLiquidity"",""outputs"":[{""internalType"":""uint256"",""name"":""amountA"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountB"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""liquidity"",""type"":""uint256""}],""stateMutability"":""nonpayable"",""type"":""function""},{""inputs"":[{""internalType"":""address"",""name"":""token"",""type"":""address""},{""internalType"":""uint256"",""name"":""amountTokenDesired"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountTokenMin"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountETHMin"",""type"":""uint256""},{""internalType"":""address"",""name"":""to"",""type"":""address""},{""internalType"":""uint256"",""name"":""deadline"",""type"":""uint256""}],""name"":""addLiquidityETH"",""outputs"":[{""internalType"":""uint256"",""name"":""amountToken"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountETH"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""liquidity"",""type"":""uint256""}],""stateMutability"":""payable"",""type"":""function""},{""inputs"":[],""name"":""factory"",""outputs"":[{""internalType"":""address"",""name"":"""",""type"":""address""}],""stateMutability"":""view"",""type"":""function""},{""inputs"":[{""internalType"":""uint256"",""name"":""amountOut"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""reserveIn"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""reserveOut"",""type"":""uint256""}],""name"":""getAmountIn"",""outputs"":[{""internalType"":""uint256"",""name"":""amountIn"",""type"":""uint256""}],""stateMutability"":""pure"",""type"":""function""},{""inputs"":[{""internalType"":""uint256"",""name"":""amountIn"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""reserveIn"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""reserveOut"",""type"":""uint256""}],""name"":""getAmountOut"",""outputs"":[{""internalType"":""uint256"",""name"":""amountOut"",""type"":""uint256""}],""stateMutability"":""pure"",""type"":""function""},{""inputs"":[{""internalType"":""uint256"",""name"":""amountOut"",""type"":""uint256""},{""internalType"":""address[]"",""name"":""path"",""type"":""address[]""}],""name"":""getAmountsIn"",""outputs"":[{""internalType"":""uint256[]"",""name"":""amounts"",""type"":""uint256[]""}],""stateMutability"":""view"",""type"":""function""},{""inputs"":[{""internalType"":""uint256"",""name"":""amountIn"",""type"":""uint256""},{""internalType"":""address[]"",""name"":""path"",""type"":""address[]""}],""name"":""getAmountsOut"",""outputs"":[{""internalType"":""uint256[]"",""name"":""amounts"",""type"":""uint256[]""}],""stateMutability"":""view"",""type"":""function""},{""inputs"":[{""internalType"":""uint256"",""name"":""amountA"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""reserveA"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""reserveB"",""type"":""uint256""}],""name"":""quote"",""outputs"":[{""internalType"":""uint256"",""name"":""amountB"",""type"":""uint256""}],""stateMutability"":""pure"",""type"":""function""},{""inputs"":[{""internalType"":""address"",""name"":""tokenA"",""type"":""address""},{""internalType"":""address"",""name"":""tokenB"",""type"":""address""},{""internalType"":""uint256"",""name"":""liquidity"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountAMin"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountBMin"",""type"":""uint256""},{""internalType"":""address"",""name"":""to"",""type"":""address""},{""internalType"":""uint256"",""name"":""deadline"",""type"":""uint256""}],""name"":""removeLiquidity"",""outputs"":[{""internalType"":""uint256"",""name"":""amountA"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountB"",""type"":""uint256""}],""stateMutability"":""nonpayable"",""type"":""function""},{""inputs"":[{""internalType"":""address"",""name"":""token"",""type"":""address""},{""internalType"":""uint256"",""name"":""liquidity"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountTokenMin"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountETHMin"",""type"":""uint256""},{""internalType"":""address"",""name"":""to"",""type"":""address""},{""internalType"":""uint256"",""name"":""deadline"",""type"":""uint256""}],""name"":""removeLiquidityETH"",""outputs"":[{""internalType"":""uint256"",""name"":""amountToken"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountETH"",""type"":""uint256""}],""stateMutability"":""nonpayable"",""type"":""function""},{""inputs"":[{""internalType"":""address"",""name"":""token"",""type"":""address""},{""internalType"":""uint256"",""name"":""liquidity"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountTokenMin"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountETHMin"",""type"":""uint256""},{""internalType"":""address"",""name"":""to"",""type"":""address""},{""internalType"":""uint256"",""name"":""deadline"",""type"":""uint256""}],""name"":""removeLiquidityETHSupportingFeeOnTransferTokens"",""outputs"":[{""internalType"":""uint256"",""name"":""amountETH"",""type"":""uint256""}],""stateMutability"":""nonpayable"",""type"":""function""},{""inputs"":[{""internalType"":""address"",""name"":""token"",""type"":""address""},{""internalType"":""uint256"",""name"":""liquidity"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountTokenMin"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountETHMin"",""type"":""uint256""},{""internalType"":""address"",""name"":""to"",""type"":""address""},{""internalType"":""uint256"",""name"":""deadline"",""type"":""uint256""},{""internalType"":""bool"",""name"":""approveMax"",""type"":""bool""},{""internalType"":""uint8"",""name"":""v"",""type"":""uint8""},{""internalType"":""bytes32"",""name"":""r"",""type"":""bytes32""},{""internalType"":""bytes32"",""name"":""s"",""type"":""bytes32""}],""name"":""removeLiquidityETHWithPermit"",""outputs"":[{""internalType"":""uint256"",""name"":""amountToken"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountETH"",""type"":""uint256""}],""stateMutability"":""nonpayable"",""type"":""function""},{""inputs"":[{""internalType"":""address"",""name"":""token"",""type"":""address""},{""internalType"":""uint256"",""name"":""liquidity"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountTokenMin"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountETHMin"",""type"":""uint256""},{""internalType"":""address"",""name"":""to"",""type"":""address""},{""internalType"":""uint256"",""name"":""deadline"",""type"":""uint256""},{""internalType"":""bool"",""name"":""approveMax"",""type"":""bool""},{""internalType"":""uint8"",""name"":""v"",""type"":""uint8""},{""internalType"":""bytes32"",""name"":""r"",""type"":""bytes32""},{""internalType"":""bytes32"",""name"":""s"",""type"":""bytes32""}],""name"":""removeLiquidityETHWithPermitSupportingFeeOnTransferTokens"",""outputs"":[{""internalType"":""uint256"",""name"":""amountETH"",""type"":""uint256""}],""stateMutability"":""nonpayable"",""type"":""function""},{""inputs"":[{""internalType"":""address"",""name"":""tokenA"",""type"":""address""},{""internalType"":""address"",""name"":""tokenB"",""type"":""address""},{""internalType"":""uint256"",""name"":""liquidity"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountAMin"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountBMin"",""type"":""uint256""},{""internalType"":""address"",""name"":""to"",""type"":""address""},{""internalType"":""uint256"",""name"":""deadline"",""type"":""uint256""},{""internalType"":""bool"",""name"":""approveMax"",""type"":""bool""},{""internalType"":""uint8"",""name"":""v"",""type"":""uint8""},{""internalType"":""bytes32"",""name"":""r"",""type"":""bytes32""},{""internalType"":""bytes32"",""name"":""s"",""type"":""bytes32""}],""name"":""removeLiquidityWithPermit"",""outputs"":[{""internalType"":""uint256"",""name"":""amountA"",""type"":""uint256""},{""internalType"":""uint256"",""name"":""amountB"",""type"":""uint256""}],""stateMutability"":""nonpayable"",""type"":""function""},{""inputs"":[{""internalType"":""uint256"",""name"":""amountOut"",""type"":""uint256""},{""internalType"":""address[]"",""name"":""path"",""type"":""address[]""},{""internalType"":""address"",""name"":""to"",""type"":""address""},{""internalType"":""uint256"",""name"":""deadline"",""type"":""uint256""}],""name"":""swapETHForExactTokens"",""outputs"":[{""internalType"":""uint256[]"",""name"":""amounts"",""type"":""uint256[]""}],""stateMutability"":""payable"",""type"":""function""},{""inputs"":[{""internalType"":""uint256"",""name"":""amountOutMin"",""type"":""uint256""},{""internalType"":""address[]"",""name"":""path"",""type"":""address[]""},{""internalType"":""address"",""name"":""to"",""type"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        var wbnbAbi =
            @"[{""constant"":true,""inputs"":[],""name"":""name"",""outputs"":[{""name"":"""",""type"":""string""}],""payable"":false,""stateMutability"":""view"",""type"":""function""},{""constant"":false,""inputs"":[{""name"":""guy"",""type"":""address""},{""name"":""wad"",""type"":""uint256""}],""name"":""approve"",""outputs"":[{""name"":"""",""type"":""bool""}],""payable"":false,""stateMutability"":""nonpayable"",""type"":""function""},{""constant"":true,""inputs"":[],""name"":""totalSupply"",""outputs"":[{""name"":"""",""type"":""uint256""}],""payable"":false,""stateMutability"":""view"",""type"":""function""},{""constant"":false,""inputs"":[{""name"":""src"",""type"":""address""},{""name"":""dst"",""type"":""address""},{""name"":""wad"",""type"":""uint256""}],""name"":""transferFrom"",""outputs"":[{""name"":"""",""type"":""bool""}],""payable"":false,""stateMutability"":""nonpayable"",""type"":""function""},{""constant"":false,""inputs"":[{""name"":""wad"",""type"":""uint256""}],""name"":""withdraw"",""outputs"":[],""payable"":false,""stateMutability"":""nonpayable"",""type"":""function""},{""constant"":true,""inputs"":[],""name"":""decimals"",""outputs"":[{""name"":"""",""type"":""uint8""}],""payable"":false,""stateMutability"":""view"",""type"":""function""},{""constant"":true,""inputs"":[{""name"":"""",""type"":""address""}],""name"":""balanceOf"",""outputs"":[{""name"":"""",""type"":""uint256""}],""payable"":false,""stateMutability"":""view"",""type"":""function""},{""constant"":true,""inputs"":[],""name"":""symbol"",""outputs"":[{""name"":"""",""type"":""string""}],""payable"":false,""stateMutability"":""view"",""type"":""function""},{""constant"":false,""inputs"":[{""name"":""dst"",""type"":""address""},{""name"":""wad"",""type"":""uint256""}],""name"":""transfer"",""outputs"":[{""name"":"""",""type"":""bool""}],""payable"":false,""stateMutability"":""nonpayable"",""type"":""function""},{""constant"":false,""inputs"":[],""name"":""deposit"",""outputs"":[],""payable"":true,""stateMutability"":""payable"",""type"":""function""},{""constant"":true,""inputs"":[{""name"":"""",""type"":""address""},{""name"":"""",""type"":""address""}],""name"":""allowance"",""outputs"":[{""name"":"""",""type"":""uint256""}],""payable"":false,""stateMutability"":""view"",""type"":""function""},{""payable"":true,""stateMutability"":""payable"",""type"":""fallback""},{""anonymous"":false,""inputs"":[{""indexed"":true,""name"":""src"",""type"":""address""},{""indexed"":true,""name"":""guy"",""type"":""address""},{""indexed"":false,""name"":""wad"",""type"":""uint256""}],""name"":""Approval"",""type"":""event""},{""anonymous"":false,""inputs"":[{""indexed"":true,""name"":""src"",""type"":""address""},{""indexed"":true,""name"":""dst"",""type"":""address""},{""indexed"":false,""name"":""wad"",""type"":""uint256""}],""name"":""Transfer"",""type"":""event""},{""anonymous"":false,""inputs"":[{""indexed"":true,""name"":""dst"",""type"":""address""},{""indexed"":false,""name"":""wad"",""type"":""uint256""}],""name"":""Deposit"",""type"":""event""},{""anonymous"":false,""inputs"":[{""indexed"":true,""name"":""src"",""type"":""address""},{""indexed"":false,""name"":""wad"",""type"":""uint256""}],""name"":""Withdrawal"",""type"":""event""}]";

        Account account = new Account(yourWalletPrivateKey, binanceChainId);
        Web3 web3 = new Web3(account, binanceTestnetNode);
        var yourWalletAddress = account.Address;

        // Step 1: We need to approve PancakeSwap router for wbnb

        // Setup function input
        Contract wbnb = web3.Eth.GetContract(wbnbAbi, wbnbAddress);
        BigInteger valueToApprove = Web3.Convert.ToWei(1000000); // Spender limit (set any)
        object[] routerApproveFunctionInput = new object[2] { pancakeSwapRouterV2AddressMainnet, valueToApprove };

        // Setup transaction 
        Function wbnbApprove = wbnb.GetFunction("approve");
        var wbnbApproveTransaction = wbnbApprove.CreateTransactionInput(yourWalletAddress, routerApproveFunctionInput);
        wbnbApproveTransaction.Gas = await wbnbApprove.EstimateGasAsync(yourWalletAddress, null, null, routerApproveFunctionInput);
        wbnbApproveTransaction.Nonce = await web3.Eth.Transactions.GetTransactionCount.SendRequestAsync(yourWalletAddress);
        wbnbApproveTransaction.GasPrice = await web3.Eth.GasPrice.SendRequestAsync();

        // Send transaction and wait for approve
        TransactionReceipt wbnbApproveResult = await wbnbApprove.SendTransactionAndWaitForReceiptAsync(wbnbApproveTransaction, functionInput: routerApproveFunctionInput);
        if (wbnbApproveResult.Status != new HexBigInteger(1))
            throw new Exception("Approve failed");

        // Step 2: Now we can swap

        // Setup function input
        var amountIn = Web3.Convert.ToWei(amount);
        var amountOutMin = Web3.Convert.ToWei(0);
        var wbnbToCake = new string[] { wbnbAddress, cakeAddress };
        var to = account.Address;
        var deadline = (uint)DateTimeOffset.UtcNow.AddSeconds(40).ToUnixTimeSeconds();
        object[] swapFunctionInput = new object[5] { amountIn, amountOutMin, wbnbToCake, to, deadline };

        // Create transaction swapExactTokensForTokens
        Contract pancakeRouter = web3.Eth.GetContract(pancakeSwapRouterV2Abi, pancakeSwapRouterV2AddressMainnet);
        Function swapFunction = pancakeRouter.GetFunction("swapExactTokensForTokens");
        var routerTransaction = swapFunction.CreateTransactionInput(yourWalletAddress, swapFunctionInput);
        routerTransaction.Gas = await swapFunction.EstimateGasAsync(yourWalletAddress, null, null, swapFunctionInput);
        routerTransaction.Nonce = await web3.Eth.Transactions.GetTransactionCount.SendRequestAsync(yourWalletAddress);
        routerTransaction.GasPrice = await web3.Eth.GasPrice.SendRequestAsync();

        // Do swap
        TransactionReceipt transactionReceiptForSwap = await swapFunction.SendTransactionAndWaitForReceiptAsync(routerTransaction, functionInput: swapFunctionInput);
        if (transactionReceiptForSwap.Status != new HexBigInteger(1))
            throw new Exception("Failed swap");
    }
}

Please note, that code runs against Mainnet, not Testnet. I wish there was more information for C# developers on web3 for things like that... Hope this gonna save time to someone.