mutator tidak berfungsi jika menggunakan method upsert

kode memanggil upsert

        PrepaidProduct::upsert($collection, ['buyer_sku_code'],
            [
                'product_name',
                'category',
                'brand',
                'type',
                'seller_name',
                'price',
                'buyer_product_status',
                'seller_product_status',
                'unlimited_stock',
                'stock',
                'multi',
                'start_cut_off',
                'end_cut_off',
                'desc',
            ]);

model

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;
use Illuminate\Support\Str;

class PostpaidProduct extends Model
{
    use HasFactory;
    use SoftDeletes;

    protected $guarded = [];

    public function setProductNameAttribute($value)
    {
        $this->attributes['product_name'] = Str::lower($value);
    }

    public function setCategoryAttribute($value)
    {
        $this->attributes['category'] = Str::lower($value);
    }

    public function setBrandAttribute($value)
    {
        $this->attributes['brand'] = Str::upper($value);
    }

    public function setSellerNameAttribute($value)
    {
        $this->attributes['seller_name'] = Str::upper($value);
    }


    public function transactions()
    {
        return $this->hasMany(TransactionPostpaid::class);
    }
}