I am trying to deploy my Node.js Express application to Vercel. My folder structure looks like this:

Index.js:

configDotenv();
const app = express();
const port = process.env.PORT || 8000;
connectDB();
connectCloudinary();

app.use(cors());
app.use(express.json());

app.get("/", (req, res) => res.send("API Working"));
app.use("/api/song", songRouter);
app.use("/api/album", albumRouter);

app.listen(port, () => console.log(`Server Port: ${port}`));

songRoute.js

const songRouter = express.Router();

songRouter.post(
  "/add",
  upload.fields([
      { name: "image", maxCount: 1 },
      { name: "audio", maxCount: 1 },
  ]),
  addSong
 );
 songRouter.get("/list", listSong);
 songRouter.delete("/remove", removeSong);

 export default songRouter;

vercel.json

{
  "version": 2,
  "builds": [
    {
      "src": "./index.js",
      "use": "@vercel/node"
    }
  ],
 "routes": [
   {
     "src": "/api/song/(.*)",
     "dest": "/index.js"
   },
   {
     "src": "/api/album/(.*)",
     "dest": "/index.js"
   },
   {
     "src": "/(.*)",
     "dest": "/index.js"
   }
 ]
}

When I deploy, I encounter errors related to routing and API handling. Can someone help me understand how to correctly configure the vercel.json file for my project?