MongoDB insertOne Replaces Documents Instead of Appending in Next.js API Route

I'm working on a Next.js API route that inserts user data into a MongoDB collection. However, whenever I insert a new document, it seems to replace all existing documents in the collection instead of appending a new one.

API Route Code (app/api/create-data/route.ts):

'use server';import { MongoClient, ServerApiVersion } from "mongodb";import { ObjectId } from "mongodb";import { NextRequest, NextResponse } from "next/server";const uri = process.env.URI;if (!uri) throw new Error("Missing MongoDB URI in environment variables");let client: MongoClient | null = null;async function connectToDB() {  if (!client) {    client = new MongoClient(uri as string, {      serverApi: {        version: ServerApiVersion.v1,        strict: true,        deprecationErrors: true,      },    });    await client.connect();    console.log("Connected to MongoDB");  }  return client;}export async function POST(req: NextRequest) {  const requestBody = await req.json();  const data = { ...requestBody, _id: new ObjectId() };  try {    const client = await connectToDB();    const db = client.db("db1");    const result = await db.collection("ewan").insertOne(data);    if (!result.acknowledged) {      throw new Error("Failed to insert document");    }    return NextResponse.json({ message: "Successfully created account", insertedId: result.insertedId });  } catch (error) {    console.error("Database error:", error);    return NextResponse.json({ error: "An error occurred while connecting to the database." }, { status: 500 });  }}

Client-Side Code (React):

const handleSubmit= async (event: React.FormEvent) => {    event.preventDefault();    const response = await fetch("/api/create-data/", {       method: "POST",      headers: {'Content-Type': 'application/json',      },      body: JSON.stringify({         email: emailRef.current.value,        password: passwordRef.current.value,        messageToStore: messageToStoreRef.current.value       })    });    const data = await response.json();    console.log("API response:", data);  };

Every time I insert a new document, it seems like it replaces all existing documents in the "ewan" collection. I expected each new document to be added instead of replacing existing ones.

What could be causing this issue?

Troubleshooting so far:

1. Checked insertOne(), which should append, not replace.
2. Verified data structure before insertion using console.log().
3. Ensured that _id is generated correctly (new ObjectId()).