Undefined variable $no_antrian

I want to create a queuing system in Laravel but I have problems with coding and don’t understand how to set up the coding correctly. Can anyone help me?

public function store(Request $request ){

        $latestAntrian = Antrian::where('layanan', $this->layanan)
            ->where('tanggal_antrian', now()->toDateString())
            ->latest('id_antrian')
            ->first();

         if (!$latestAntrian) {
            if($this->layanan === 'anak'){
                $this->no_antrian = 'A1';
            } elseif ($this->layanan === 'ibu'){
                $this->no_antrian = 'B1';
            } elseif ($this->layanan === 'lansia'){
                $this->no_antrian = 'C1';
            }
            $this->tanggal_antrian = now()->toDateString();
        } else {

            $kode_awal = substr($latestAntrian->no_antrian, 0, 1);
            $angka = (int) substr($latestAntrian->no_antrian, 1);
            $angka +=1;
            $no_antrian = $kode_awal . $angka;
            $tanggal_antrian = $latestAntrian->tanggal_antrian;
        }

        $data                   = new Antrian;
        $data->no_antrian       = ($no_antrian);
        $data->nama             = $request->get('nama');
        $data->no_hp            = $request->get('no_hp');
        $data->layanan          = $request->get('layanan');
        $data->tanggal_antrian  = ($tanggal_antrian);
        $data->save();
   
         Alert::success('Data Berhasil Ditambah');
 
         return redirect()->route('antrianuser')->with([
             'success' => 'Data Berhasil Di Tambah'
         ]);
    }

help me by improving this code