"message": "Cannot read property 'firstName' of undefined" - node.js

Question

I am trying to build a rest API with node express and MongoDB, when I try to test my API with postman I getting this response
"message": "Cannot read property 'firstName' of undefined"
bellow I have attached all my server-side code. first, I have config my application with mongo and started developing the models and respective controllers for that model. inside the controller, I have defined my get and post methods. I don't understand why I am getting that response message when I try to send a post request.
Server Config
import Express from "express";
import Mongoose from "mongoose";
import CorsOptions from "cors";
import bodyParser from "body-parser";
import apiRoutes from "./routes/api.js";
const app = Express();
app.use("/api", apiRoutes);
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
const CONNECTION_URL =
"mongodb+srv://user:Index-123#cluster0.uhijm.mongodb.net/SustainableIQ?retryWrites=true&w=majority";
const PORT = process.env.PORT || 5000;
Mongoose.connect(CONNECTION_URL)
.then(() =>
app.listen(PORT, () => console.log("server running on port: ${PORT}"))
)
.catch((error) => console.log(error.message));
Routes
import Express from "express";
import {
getApi,
createUser,
adminCreate,
} from "../controller/UserController.js";
const router = Express.Router();
router.get("/", getApi);
router.post("/create", createUser);
router.post("/create-admin", adminCreate);
export default router;
Nodejs Controller
import postUser from "../models/postUser.js";
import adminSchema from "../models/adminUser.js";
export const getApi = async (req, res) => {
try {
postUser
.find()
.exec()
.then((result) => {
if (result) {
res.status(200).json(result);
}
});
} catch (error) {
res.status(404).json({ message: error.message });
}
};
export const adminCreate = async (req, res) => {
try {
const admin = req.body;
const newAdmin = new adminSchema(admin);
newAdmin.firstName = req.body.firstName;
newAdmin.secondName = req.body.secondName;
await newAdmin.save();
res.status(201).json(newAdmin);
} catch (err) {
res.status(409).json({ message: err.message });
}
};
export const createUser = async (req, res) => {
try {
const post = req.body;
const newPost = new postUser(post);
newPost.firstName = req.body.firstName;
newPost.secondName = req.body.secondName;
newPost.position = req.body.position;
newPost.compnayName = req.body.compnayName;
newPost.contactNumber = req.body.contactNumber;
newPost.email = req.body.email;
await newPost.save();
res.status(201).json(newPost);
} catch (err) {
res.status(409).json({ message: err.message });
}
};
mongodb schema
import Mongoose from "mongoose";
var adminSchema = Mongoose.Schema({
firstName: { type: String, required: true },
secondName: { type: String, required: true },
createdAt: {
type: Date,
default: Date.now,
},
});
var adminSchema = Mongoose.model("adminSchema", adminSchema);
export default adminSchema;