Read and Write in Next Js Is not working in production (vercel)

import { NextResponse } from "next/server";
import { promises as fs } from "fs";
import path from "path";
type dbSchema = {
  pageView: number;
  printResume: number;
  savePdf: number;
};
export async function GET() {
  const jsonDirectory = path.join(process.cwd(), "json");
  const data = await fs.readFile(process.cwd() + "/public/db.json", "utf-8");
  const dataInJson = JSON.parse(data);
  return NextResponse.json(dataInJson);
}
export async function POST(req: Request) {
  const data = (await req.json()) as { type: "print" | "view" | "save" };
  let db = await ReadDb();
  const dbJson = JSON.parse(db) as dbSchema;
  if (data.type === "print") {
    dbJson.printResume = dbJson.printResume + 1;
  } else if (data.type === "save") {
    dbJson.savePdf = dbJson.savePdf + 1;
  } else if (data.type === "view") {
    dbJson.pageView = dbJson.pageView + 1;
  }
  SaveDb(dbJson);
  return NextResponse.json({ status: "Ok" });
}
async function ReadDb() {
  const jsonDirectory = path.join(process.cwd(), "json");
  const db = await fs.readFile(process.cwd() + "/public/db.json", "utf-8");

  return db;
}
async function SaveDb(newDb: dbSchema) {
  const db = await fs.writeFile(
    process.cwd() + "/public/db.json",
    JSON.stringify(newDb)
  );
}