Sum pivot table field on Eloquent many-to-many relationship

I have an orders table, an items table, and a pivot table called item_order which has two custom fields (price, quantity). The relationship between Order and Item is belongsToMany. I'm trying to return the count of all items with an id of 1, where the parent Order->status == 'received'. For the life of me, I can't figure out how to do this.

class Order extends Model
{
    public function items()
    {
        return $this->belongsToMany(Item::class)->withPivot('price', 'quantity');
    }
}

class Item extends Model
{
    public function orders()
    {
        return $this->belongsToMany(Order::class)->withPivot('price', 'quantity');
    }
}

via Chebli Mohamed