BadMethodCallException in Laravel-admin after adding accessor to model

After adding a accessor to my model, laravel-admin shows an above error when creating a post.

BadMethodCallException In ForwardsCalls.php line 71 : Call to undefined method App\Models\Post::coverUrl()

First few line of App\Models\Post.php:

<?php

namespace App\Models;

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

class Post extends Model {
    use HasFactory;

    protedted function coverUrl(): Attribute
    {
        return Attribute::make(
            get: fn ( $value) => str_replace(' ','%20',$value),
        );
    }

I've searched for hours, never found the same case. All of a sudden, this solution just came to my mind and it worked!
Change protedted function coverUrl(): Attribute to public function coverUrl(): Attribute.