incr/app/Models/Milestone.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;

/**
 * @method static create(array $array)
 * @method static orderBy(string $string)
 */
class Milestone extends Model
{
    protected $fillable = [
        'tracker_id',
        'target',
        'description',
    ];

    protected $casts = [
        'target' => 'integer',
    ];

    public function tracker(): BelongsTo
    {
        return $this->belongsTo(Tracker::class);
    }
}