I am trying to connect my nextjs project with mongo db i am not able to do it. I am using mongodb compass i have added this to the .env file MONGODB_URI="mongodb://localhost:27017/testingreels" here is my lib->db.ts file

import mongoose from "mongoose";

const MONGODB_URI = process.env.MONGODB_URI!;

if (!MONGODB_URI) {
  throw new Error(
    "Please define the MONGODB_URI environment variable inside .env.local"
  );
}

let cached = global.mongoose;

if (!cached) {
  cached = global.mongoose = { conn: null, promise: null };
}

export async function connectToDatabase() {
  if (cached.conn) {
    return cached.conn;
  }

  if (!cached.promise) {
    const opts = {
      bufferCommands: true,
      maxPoolSize: 10,
    };

    cached.promise = mongoose
      .connect(MONGODB_URI, opts)
      .then(() => mongoose.connection);
  }

  try {
    cached.conn = await cached.promise;
    console.log("connected to database")
} catch (e) {
    cached.promise = null;
    console.log("cannot connect to database")
    throw e;
  }

  return cached.conn;
}

and i have api/auth/register/route.ts

import { NextRequest, NextResponse } from "next/server";
import { connectToDatabase } from "@/lib/db";
import User from "@/models/Users";

export async function POST(request: NextRequest) {
  try {
    const { email, password } = await request.json();

    if (!email || !password) {
      return NextResponse.json(
        { error: "Email and password are required" },
        { status: 400 }
      );
    }

    await connectToDatabase();

    // Check if user already exists
    const existingUser = await User.findOne({ email });
    if (existingUser) {
      return NextResponse.json(
        { error: "Email already registered" },
        { status: 400 }
      );
    }

    await User.create({
      email,
      password,
    });

    return NextResponse.json(
      { message: "User registered successfully" },
      { status: 201 }
    );
  } catch (error) {
    console.error("Registration error:", error);
    return NextResponse.json(
      { error: "Failed to register user" },
      { status: 500 }
    );
  }
}

when i am using the postman to test 500 error is coming and database is also not connecting