Just return the fee values, no mutating

utils/estimateFee.ts

@@ -1,19 +1,24 @@
-import { sign, XRPL_Account } from "xrpl-accountlib"
-import state from "../state"
+import { derive, sign } from "xrpl-accountlib"
+import state, { IAccount } from "../state"
 
-// Mutate tx object with network estimated fee value
-const estimateFee = async (tx: Record<string, unknown>, keypair: XRPL_Account): Promise<null | { base_fee: string, median_fee: string; minimum_fee: string; open_ledger_fee: string; }> => {
+const estimateFee = async (tx: Record<string, unknown>, account: IAccount): Promise<null | { base_fee: string, median_fee: string; minimum_fee: string; open_ledger_fee: string; }> => {
   const copyTx = JSON.parse(JSON.stringify(tx))
+  console.log(tx)
   delete copyTx['SigningPubKey']
+  if (!copyTx.Fee) {
+    copyTx.Fee = '1000'
+  }
+  const keypair = derive.familySeed(account.secret)
   const { signedTransaction } = sign(copyTx, keypair);
   try {
     const res = await state.client?.send({ command: 'fee', tx_blob: signedTransaction })
     if (res && res.drops) {
-      return tx['Fee'] = res.drops.base_fee;
+      return res.drops;
     }
     return null
   } catch (err) {
-    throw Error('Cannot estimate fee')
+    throw Error('Cannot estimate fee');
+    return null
   }
 }