fix: declared return type on getExchangeRate

src/transaction/transaction.controller.ts

@@ -1,5 +1,5 @@
 import { Controller, Post, UsePipes, Body } from '@nestjs/common';
-import { ExchangeRateInput } from 'src/exchange-rate/exchange-rate.dto';
+import { ExchangeRateInput, ExchangeRateResponse } from 'src/exchange-rate/exchange-rate.dto';
 import { ExchangeRateService } from 'src/exchange-rate/exchange-rate.service';
 import { TransactionService } from './transaction.service';
 import { transactionBodySchema } from './transaction.validation';
@@ -112,7 +112,7 @@ export class TransactionController {
   }
 
   getExchangeRate(exchangeRateInput: ExchangeRateInput) {
-    return new Promise((resolve, reject) => {
+    return new Promise<ExchangeRateResponse>((resolve, reject) => {
       try {
         this.exchangeRateService.convertCurrency(exchangeRateInput).subscribe({
           next: resolve,