Attempt to read property "name" on null and $book->category?->name result in one record show data and other record not shown this data(table filled)

I have this one to many problems with table of books and categories on my laravel project.

three data I insert two of which is had same category column value with the corresponding id of said categories.

before I insert third data it was fine, but after I insert third data it show:

Attempt to read property "name" on null

I tried $book->category?->name and resulted in two previous data had category name appear but not the third, is there something wrong with my code of relation or what?

Categories.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\HasMany;
use App\Models\Book;

class Categories extends Model
{
    use HasFactory;
    public function book(): HasMany
    {
        return $this->hasMany(Book::class, 'category');
    }
    protected $fillable = [
        'name',
    ];
}

Book.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use App\Models\User;
use App\Models\Rent;
use App\Models\Categories;
use Illuminate\Database\Eloquent\Relations\HasMany;
use Illuminate\Database\Eloquent\Relations\BelongsTo;

class Book extends Model
{
    use HasFactory;
    public function categories(): belongsTo
    {
        return $this->belongsTo(Categories::class, 'id');
    }
    protected $fillable = [
        'book_code',
        'book_title',
        'author',
        'category',
        'publisher',
        'stock',
        'book_cover',
        'book_desc',
        'barcode',
    ];
}

book/index.blade.php

@foreach ($book as $book)
    <tr>
        <td><img src="/{{ $book->book_cover }}" width="100px"></td>
        <td>{{ $book->book_title }}</td>
        <td>{{ $book->categories?->name }}</td>
        <td>{{ $book->stock }}</td>
        <td>
            <form action="{{ route('book.destroy',$book->id) }}" method="Post">
            <a class="btn btn-success" href="{{ route('book.show',$book->id) }}">Detail</a>    
            <a class="btn btn-warning" href="{{ route('book.edit',$book->id) }}">Edit</a>
                @csrf
                @method('DELETE')
                <button type="submit" class="btn btn-danger">Hapus</button>
            </form>
        </td>
    </tr>
@endforeach

Is there something wrong with my code that resulted in category name record shown on first and second record of book insert but not third record of book?

Always name the Model name as a singular name so it should be Category not Categories.

Can you please try this function in your model?

Category.php

public function books() 
{       
    return $this->hasMany(Category::class,'id');
 }

Book.php

public function categories()
{
    return $this->belongsTo(Book :: class,'category','id');
}