Laravel 5.8: The items.0.id field is required. Error

I am working on an application for the company I work for, this application was made using Laravel 5.8 and MySQL. I have managed to incorporate improvements and so on but there is something that I still can't solve (I'm a junior programmer and I still don't have that much experience). The issue is that there is a many-to-many relationship, I need to make it possible to link new items to the project with their respective quantities in the edit view of a project, in turn it should be possible to unlink previously related items if needed. But nevertheless when trying to do it, the view responds to me with the following error: The items.0.id field is required.The items.0.quantity field is required.

Below the code:

ProjectController:

public function edit($id)
    {
        $project = Project::findOrFail($id);
        $items = Item::all();
        $project_items = $project->items()->pluck('id')->toArray();
        $project_items_quantity = $project->items()->pluck('quantity', 'id')->toArray();
        $item_project = ItemProject::where('project_id', $id)->get();

        return view('includes.edit_delete_project',
            compact('items', 'project_items', 'project_items_quantity', 'item_project'))
            ->with(['project'=> Project::getProjectById($id),
            'entities'=>Entity::getEntities(),
                'countries'=>Country::getCountries()]);
    }

    public function update(Request $request, Project $project)
    {
        $this->validate($request, array(
            'code' => 'required|string|max:255',
            'entity' => 'required|string|max:255',
            'country' => 'required|string|max:255',
            'items' => 'nullable|array',
            'items.*.id' => 'required|integer|exists:items,id',
            'items.*.quantity' => 'required|integer|min:0',
        ));

        $project->update($request->only(['code', 'entity', 'country']));

        if ($request->has('items')) {
            $items = $request->input('items');

            $currentItems = $project->items->pluck('id')->toArray();
            $detachItems = array_diff($currentItems, array_column($items, 'id'));
            $project->items()->detach($detachItems);

            foreach ($items as $item) {
                $project->items()->syncWithoutDetaching([$item['id'] => ['quantity' => $item['quantity']]]);
            }
        }

        return response()->json($project);
    }

Project Model:

class Project extends Model
{
    protected $table = "project";

    protected $fillable = ['code',
        'entity',
        'country'];
    protected $hidden = ['id'];

    public static function getProjects()
    {
        return Project::all();
    }

    public static function getProjectById($id)
    {
        return Project::find($id);
    }

    public function items()
    {
        return $this->belongsToMany(Item::class, 'project_item',
            'project_id', 'item_id')->withPivot('quantity');
    }
}

Project edit view:

<!-- Edit -->
<div class="modal fade" id="edit">
    <div class="modal-dialog modal-lg" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span></button>
                <h4 class="modal-title"><b><span class="employee_id">Edit Project</span></b></h4>
            </div>
            <div class="modal-body">
                <form class="form-horizontal" method="POST" action="/includes/edit_delete_project/">
                    @csrf
                    <div class="form-group">
                        <label for="code" class="col-sm-3 control-label"><span style="color: red">*</span> Code</label>

                        <div class="col-sm-9">
                            <input oninput="this.value = this.value.toUpperCase()" type="text" class="form-control"
                                   id="code" name="code" value="" required>
                        </div>
                    </div>
                    <div class="form-group">
                        <label for="entity" class="col-sm-3 control-label"><span style="color: red">*</span> Company</label>

                        <div class="col-sm-9">
                            <select class="form-control" id="entity" name="entity" required>
                                <option value="" selected></option>
                                @foreach($entities as $entity)
                                    <option value=""> </option>
                                @endforeach
                            </select>
                        </div>
                    </div>
                    <div class="form-group">
                        <label for="country" class="col-sm-3 control-label"><span style="color: red">*</span> Country</label>

                        <div class="col-sm-9">
                            <select class="form-control" id="country" name="country" required>
                                <option value="" selected></option>
                                @foreach($countries as $country)
                                    <option value=""> </option>
                                @endforeach
                            </select>
                        </div>
                    </div>


                    <div class="form-group">
                        <label for="items" class="col-sm-3 control-label"><span style="color: red"></span> Items</label>

                        <div class="col-sm-9">
                            @foreach($items as $item)
                                <div class="form-check">
                                    <input type="checkbox" class="form-check-input" name="items[]" value="" id="item">
                                    <label class="form-check-label" for="item"> - </label>

                                    <input type="number"
                                           class="form-control"
                                           min="1"
                                           style="width: 100px;"
                                           id="quantity_"
                                           name="quantity_"
                                           value="" placeholder="Quantity">
                                </div>
                            @endforeach
                        </div>
                    </div>

                    <div class="modal-footer">
                        <button type="button" class="btn btn-default btn-flat pull-left" data-dismiss="modal"><i
                                class="fa fa-close"></i> Close
                        </button>
                        <button type="submit" class="btn btn-success btn-flat" name="edit"><i class="fa fa-check-square-o"></i>
                            Update
                        </button>
                    </div>
                </form>
            </div>
        </div>
    </div>
</div>

I have tried various recommendations from the internet but still have not been successful with any. It is the only thing that I need of all that they asked me to finish the application. I just need to solve what I exposed at the beginning and I will be very grateful to anyone who can help me.

via Chebli Mohamed