How to display the index of a tag, not its name?

Question

Laravel

Welcome all. I am familiar with laravel and relationships.
There is html, a list of categories is displayed here. Typical CRUD application.

<select class="form-control select2" multiple="" data-placeholder="Select a State"
                                            style="width: 100%;" name="categories[]" tabindex="-1" aria-hidden="true">
                                        @foreach($categorys as $category)
                                            <option value="{{ $category->id }}">{{ $category->name }}</option>
                                        @endforeach
                                    </select>

Next controller to write to DB

$post = post::find($id);
        $post->fill($req->all());
        $post->categories()->sync($req->categories);
        $post->save();

Question:
Why if I check the answer $req->all() it outputs "categories": ["Ghbdtn"] and not "categories": ["1"] ? Because of this, do not write to the DB.

Answer 1

Check what you have in the value of the select. The array must contain values ​​from this attribute.