how to add value quantiy to array - laravel

Question

I have the following code, you can go through Class Livewire and View Livewire, I got the desired result but I want to add 1 key to the half to collect, the key I want is quantity, when entering the quantity it will add to collect for me
Class Livewire
<?php
namespace App\Http\Livewire;
use App\Models\Medicine;
use App\Models\MedicineCategory;
use Livewire\Component;
class SelectMedicineCategoryTable extends Component
{
public $columns = ['STT', 'Name', 'Qty', 'Unit'];
public $medicines;
public array $selectedMedicineArray = [];
public $getAllMedicineCategory;
public $selectMedicineCategoryId = null;
public $quantity = [];
public function render()
{
$this->getAllMedicineCategory = MedicineCategory::where('status', MedicineCategory::ACTIVE)->get(['id', 'name_medicine']);
if ($this->selectMedicineCategoryId != '') {
$this->medicines = Medicine::where('status', Medicine::ACTIVE)->Where('medicine_category_id', $this->selectMedicineCategoryId)->get(['id', 'name', 'unit']);
} else {
$this->medicines = [];
}
return view('livewire.select-medicine-category-table');
}
}
View livewire
#forelse ($medicines as $item)
<tr>
<td><input class="form-check-input" type="checkbox" wire:model="selectedMedicineArray"
id="" value="{{ $item }}">
<td>{{ $loop->iteration }}</td>
</td>
<td>{{ $item->name }}</td>
<td><input type="number" wire:model="quantity.{{ $item->id }}" min="1"
id="" value="1">
</td>
<td>{{ $item->unit }}</td>
</tr>
#empty
<tr>
<td>Not found result</td>
</tr>
#endforelse
Output current
array ( 0 => '{"id":1,"name":"Padamon","unit":"V\\u0129"}', )
I want Output
array ( 0 => '{"id":1,"name":"Padamon","unit":"V\\u0129", 'quantity:...'}', )