Server can not perform JWT Authentication Request on MERN

Question

I was working on a MERN app and was trying to use jason web-token (JWT) and bcrypt for authentication. It uses two routes for signup and authentication. However, I'm getting an internal server error coming from admin route not sure though. I have not been able to connect to the frontend correctly because of that.

//admin model
const mongoose = require('mongoose');
const jwt = require('jsonwebtoken');
const Joi = require('joi');
const passwordComplexity = require('joi-password-complexity');

const AdminSchema = new mongoose.Schema({
    name: { type: String, required:true },
    email: { type: String, required:true, unique:true  },
    password: { type: String, required:true,  },
    
});

AdminSchema.methods.generateAuthToken = function(){
    const token=jwt.sign({_id:this._id}, process.env.JWTPRIVATEKEY,{expiresIn: "7d",});
    return token;
}

const AdminModel = mongoose.model("admin", AdminSchema)

const validate=(data) =>{
    const schema= Joi.object({
        name:Joi.string().required().label("Name"),
        email:Joi.string().email().required.label("Email"),
        password:passwordComplexity().required().label("Password")
    });
    return schema.validate(data)
};
module.exports = {AdminModel, validate};
//module.exports = AdminModel;

//admin route
const router= require("express").Router();
const {AdminModel, validate} = require("../models/admin");
const bcrypt = require("bcrypt");

router.post("/", async(req,res) =>{
  try {
    const {error} = validate(req.body);
    if(error)
      return res.status(400).send({message: error.details[0].message});
    const user = await AdminModel.findOne({email: req.body.email});
    if(user)
      return res.status(409).send({message:"Admin with given email exists"});
    const salt = await bcrypt.genSalt(Number(process.env.SALT));
    const hashPassword = await bcrypt.hash(req.body.password, salt);
    await  new AdminModel({ ...req.body, password:hashPassword}).save();
    res.status(201).send({message:"Admin created successfully"})
  } catch (error) {
    res.status(500).send({message:"Internal Server Error YOu see"})
  }
})
module.exports = router;

//adminAuthentication route
const router = require("express").Router();
const {AdminModel} = require("../models/admin");
const bcrypt = require("bcrypt");
const Joi = require("joi");

router.post("/", async (req, res) => {
    try {
        const { error } = validate(req.body);
        if (error)
            return res.status(400).send({ message: error.details[0].message });

        const Admin = await AdminModel.findOne({ email: req.body.email });
        if (!Admin)
            return res.status(401).send({ message: "Invalid Email or Password" });

        const validPassword = await bcrypt.compare(
            req.body.password,
            Admin.password
        );
        if (!validPassword)
            return res.status(401).send({ message: "Invalid Email or Password" });

        const token = Admin.generateAuthToken();
        res.status(200).send({ data: token, message: "logged in successfully" });
    } catch (error) {
        res.status(500).send({ message: "Internal Server Error" });
    }
});

const validate = (data) => {
    const schema = Joi.object({
        email: Joi.string().email().required().label("Email"),
        password: Joi.string().required().label("Password"),
    });
    return schema.validate(data);
};

module.exports = router;