liwo/app/Models/Cost.php

<?php

namespace App\Models;

use App\Models\Model;

class Cost extends Model
{
    public const USER_TYPE = 'users';

    public const FILE_TYPE = 'files';

    public $perPage = 12;

    protected $fillable = [
        'business_id', 'type', 'month', 'amount', 'fee', 'duration','cost','tax', 'additional'
    ];

    public $casts = [
        'additional' => 'array',
        'tax' => 'float',
    ];

    public function business()
    {
        return $this->belongsTo(Business::class, 'business_id');
    }
}