how to use Laravel Rinvex Attributes?

I'm trying to use https://github.com/rinvex/attributes, and can't understand how. Docs are not clear for me and i need help.

After installing the package i've done next:

I have \App\Models\Product class that i want to make attributable. So I put in model

use Rinvex\Attributes\Traits\Attributable;

class Product extends Model
{
    use CrudTrait;
    use Sluggable;
    use Attributable;

/***/

In AppServiceProvider's boot():

app('rinvex.attributes.entities')->push(App\Models\Product::class);

Next - just like in docs - creating the attribute in Tinker console just like that:

app('rinvex.attributes.attribute')->create([
    'slug' => 'size',
    'type' => 'varchar',
    'name' => 'Product Size',
    'entities' => ['App\Models\Product'],
]);

In DB i see added entries in attributes_entries and attributes tables.

But when i try to call

$product->size = 50;
$product->save(); - got "not found field in Model".

What do i do wrong?

via Chebli Mohamed