Unable to post data to a collection in mongodb database - node.js

Question

I am working with mongodb right now for creating an android app using react native.My problem is i am not able to post data to collection in mongodb.
My app.js code
const express = require("express");
const app = express();
const morgan = require("morgan");
const mongoose = require("mongoose");
const cors = require("cors");
require("dotenv/config");
app.use(cors());
app.options("*", cors());
//middleware
app.use(express.json());
app.use(morgan("tiny"));
//Routes
const categoriesRoutes = require("./routes/categories");
const productsRoutes = require("./routes/products");
const usersRoutes = require("./routes/users");
const ordersRoutes = require("./routes/orders");
const api = process.env.API_URL;
app.use(`${api}/categories`, categoriesRoutes);
app.use(`${api}/products`, productsRoutes);
app.use(`${api}/users`, usersRoutes);
app.use(`${api}/orders`, ordersRoutes);
//Database
mongoose
.connect(process.env.CONNECTION_STRING, {
useNewUrlParser: true,
useUnifiedTopology: true,
dbName: "eshop-database",
})
.then(() => {
console.log("Database Connection is ready...");
})
.catch((err) => {
console.log(err);
});
//Server
app.listen(3000, () => {
console.log("server is running http://localhost:3000");
});
My categories.js:
const {Category} = require('../models/category');
const express = require('express');
const router = express.Router();
router.get('/', async (req, res) =>{
const categoryList = await Category.find();
if(!categoryList) {
res.status(500).json({success: false})
}
res.send(categoryList);
})
router.post('/', async (req,res)=>{
let category = new Category({
name: req.body.name,
icon: req.body.icon,
color: req.body.color
})
category = await category.save();
if(!category)
return res.status(404).send('The category cannot be created!')
res.send(category);
})
module.exports = router;
My category.js:
const mongoose = require('mongoose');
const categorySchema = mongoose.Schema({
name: {
type: String,
required: true,
},
icon: {
type: String,
},
color: {
type: String,
}
})
exports.Category = mongoose.model('Category', categorySchema);
Through postman tool i checked it but there is no error even though i am unable to post the data and in mongodb database it is displaying as Query Results: 0