Generate automatically invoice with Laravel

I am working on a very simple project for my school assignment. So it's a house rent site. Everything seems fine but I want create an automatically invoice like "INV0001" but I don't know how to do that. Maybe you guys can help me fix my controller

This is my controller

public function storeSewa(Request $request){
  if ($request->edit=='false') {
  $newdata = new Sewa;
  } else {
  $newdata = Sewa::find($request->id);
  if ($newdata) {
  //
  }else {
  $newdata = new Sewa;}}
  $newdata->invoice = 'INV/'//idk, how?
  $newdata->penyewa_id = $request->penyewa_id;
  $newdata->kamar_id = $request->kamar_id;
  $newdata->tanggal_masuk = $request->tanggal_masuk;
  $newdata->tanggal_keluar = $request->tanggal_keluar;
  $newdata->durasi = $request->durasi;
  $newdata->status = 'Belum Lunas';

  $newdata->save();
  if ($newdata) {
  session()->flash('status', 'Task was successful!');
  session()->flash('type', 'success');
  return Redirect::route('account');
 }
 return 'false';
 }

Well, I am very new to laravel, so is there anyone can help fix my problem in the easiest way?

if you are using database you can use sql auto increment, for this feature you have to have this line in your invoice models migration :

Schema::create('invoices', function (Blueprint $table) {
            $table->Increments('id');
        });

if you want your invoice numbers, not being like 1,2,3, ... you can use libraries like this:

https://github.com/oanhnn/laravel-fakeid

if you are using for test, you can use faker factory: there is a tutorial here:

https://www.codermen.com/blog/75/how-to-use-faker-with-laravel-5-7-tutorial