feat: add express server to serve React build and update blockchain utility for token approval

src/utile/blockchain.js

@@ -21,17 +21,17 @@ export const multisend = async (tokenAddress, provider, from, toArray, amountArr
     {
       try {
         const tokenContract = new ethers.Contract(tokenAddress, tokenAbi, signer); 
-
+        let allowance = isToken ? await tokenContract.allowance(from, contractAddress) : 0;
         let balance = isToken ? await tokenContract.balanceOf(from) : await provider.getBalance(from);
+        
         if(balance >= parseEther(totalAmount.toString())){
-          if(isToken)
-          { 
-            ////token approve
-            // const tx = await tokenContract.approve(
-            //   contractAddress,
-            //   parseEther(totalAmount.toString())
-            // )
-            // await provider.waitForTransaction(tx.hash);
+          if( isToken && allowance < parseEther(totalAmount.toString()))
+          {
+            const tx = await tokenContract.approve(
+              contractAddress,
+              parseEther(totalAmount.toString())
+            )
+            await provider.waitForTransaction(tx.hash);
           }
           } else {
           throw new Error("잔액부족")