Save data and attach at same time in Laravel

I have a blog app that I need to add tags on post. I have an input field, post model, tag model and 3 tables on database: posts, tags and tag_post with ManyToMany relationship.

When I try to add new tag on table, it send to tag_post table and not tag table. I did trying change my model and controller but it worse.

Post Model

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{

  protected $filliable = ['PostTitle', 'post', 'slug'];

  public function categories()
  {
    return $this->BelongsToMany('App\Categories', 'category_post');
  }

  public function tags()
  {
    return $this->BelongsToMany('App\Tag', 'tag_post');
  }

}

Tag Model

namespace App;

use Illuminate\Database\Eloquent\Model;

class Tag extends Model
{
    protected $filliable = ['tag'];


    public function posts()
    {
      return $this->BelongsToMany('App\Post', 'tags_post');
    }
}

PostController

public function store(Request $request)
{

    $post = new Post;
    $post->user_id = auth::id();
    $post->PostTitle = $request->PostTitle;
    $post->post = $request->post;
    $post->slug = $request->slug;
    $post->status = '1';
    $post->save();
    $post->categories()->attach($request->categories);

      $tags = new Tag;
    foreach($tags as $tag){
    $tags->tag = $request->tags;
    if($tags->save()){
      $post->tags()->attach($request->tags);
    }
  }

    return redirect('blog')->with('messageSuccess', '¡Tu entrada se ha creado Exitosamente!');
}

Form

<div class="post-panel-3">
            <div class="form-group">
              <label for="postTags">Etiquetas: </label>

              <input  type="text" name="tags[]" value=" " class="form-control" placeholder="Etiquetas" id="tagBox">

            </div>

I edit the if statement but i have this error when i save tags Type error: Argument 1 passed to Illuminate\Database\Grammar::parameterize() must be of the type array, string given, called in C:\laragon\www\asiviajo-app\vendor\laravel\framework\src\Illuminate\Database\Query\Grammars\Grammar.php on line 665

via Johanng1993