example-code/php-laravel/app/Models/Referral.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

use App\Models\User;

class Referral extends Model
{
    use HasFactory;

	public function users() {
		return $this->hasMany(User::class);
	}
}