Issue running express in MERN stack - express

Question

This is the error I got on running npm start:
F:\Works\Projects\Node\Voice_pres_withbackend\api\node_modules\express\lib\router\index.js:458
throw new TypeError('Router.use() requires a middleware function but got a ' + gettype(fn))
^
TypeError: Router.use() requires a middleware function but got a string
at Function.use (F:\Works\Projects\Node\Voice_pres_withbackend\api\node_modules\express\lib\router\index.js:458:13)
at Function.<anonymous> (F:\Works\Projects\Node\Voice_pres_withbackend\api\node_modules\express\lib\application.js:220:21)
at Array.forEach (<anonymous>)
at Function.use (F:\Works\Projects\Node\Voice_pres_withbackend\api\node_modules\express\lib\application.js:217:7)
at Object.<anonymous> (F:\Works\Projects\Node\Voice_pres_withbackend\api\app.js:25:5)
at Module._compile (internal/modules/cjs/loader.js:956:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:973:10)
at Module.load (internal/modules/cjs/loader.js:812:32)
at Function.Module._load (internal/modules/cjs/loader.js:724:14)
at Module.require (internal/modules/cjs/loader.js:849:19)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! api#0.0.0 start: `node ./bin/www`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the api#0.0.0 start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm ERR! A complete log of this run can be found in:
npm ERR! C:\Users\HP\AppData\Roaming\npm-cache\_logs\2020-09-21T14_50_24_855Z-debug.log
This is part of the code the error is pointing to :
var express = require("express");
var router = express.Router();
router.get("/", function (req, res) {
res.send("Api successful");
});
module.exports = router;
Can you please tell me what it is that I'm doing wrong?