Symfony \ Component \ HttpKernel \ Exception \ MethodNotAllowedHttpException comes up as I do the following things

This is my web.php file where my resource route is present!

Route::group(['namespace' => 'Admin'],function()
{
    Route::resource('admin/post','PostController');
});

Here is the post controller function store which is storing my data to the database and the showing it to the panel, it was working fine but after I added the categories and tags requests it just broke up!!

public function store(Request $request)
    {
        $this->validate($request,
            [
                'title' => 'required',
                'subtitle' => 'required',
                'slug' => 'required',
                'body' => 'required'
            ]);
        $post = new post;
        $post->title = $request->title;
        $post->subtitle = $request->subtitle;
        $post->slug = $request->slug;
        $post->body = $request->body;
        $post->save();
        $post->tags()->sync($request->tags);
        $post->categories()->sync($request->categories);
        return redirect(route('post.index'));
    }

As I clicked the submit button in this form below:

<form role="form" action="" method="post">
            
            
              <div class="box-body">
                <div class="col-lg-6">
                  <div class="form-group">
                    <label for="title">Post Title</label>
                    <input type="text" class="form-control" id="title" name="title" placeholder="Welcome to the world of reality">
                  </div>
                  <div class="form-group">
                    <label for="subtitle">Post Sub Title</label>
                    <input type="text" class="form-control" id="subtitle" name="subtitle" placeholder="Here we can grow together">
                  </div>
                  <div class="form-group">
                    <label>Select Tags</label>
                    <select class="form-control select2 select2-hidden-accessible" multiple="" data-placeholder="Select a State" style="width: 100%;" tabindex="-1" aria-hidden="true" name="tags[]">
                      @foreach ($tags as $tag)
                        <option value=""></option>
                      @endforeach
                    </select>
                  </div>
                  <div class="checkbox">
                    <label>
                      <input type="checkbox" name="status"> Publish
                    </label>
                  </div>
                </div>
                <div class="col-lg-6">
                  <div class="form-group">
                    <label for="slug">Post Slug</label>
                    <input type="text" class="form-control" id="slug" name="slug" placeholder="Slug"}}">
                  </div>
                  <div class="form-group">
                    <label>Select Categories</label>
                    <select class="form-control select2 select2-hidden-accessible" multiple="" data-placeholder="Select a State" style="width: 100%;" tabindex="-1" aria-hidden="true" name="categories[]">
                      @foreach ($categories as $category)
                        <option value=""></option>
                      @endforeach
                    </select>
                  </div>
                  <div class="form-group">
                    <label for="image" style="margin-top: 10px;">File input</label>
                    <input type="file" name="image" id="image">
                  </div>
                </div>
              </div>
              <!-- /.box-body -->
              <div class="box box-info">
              <div class="box-header">
                <h3 class="box-title">Write Post Body Here
                  <small>(Advanced and full of features)</small>
                </h3>
                <!-- tools box -->
                <!-- /. tools -->
              </div>
              <!-- /.box-header -->
              <div class="box-body pad">
                <textarea id="editor1" name="body" rows="10" cols="80">
                  Here you can write your post.
                </textarea>
              </div>
          </div>
              <div class="box-footer">
                <button type="submit" class="btn btn-primary">Submit</button>
                <a href="" class="btn btn-warning">Back</a>
              </div>
            </form>

I don't know what is going on why it do this, I also have the update function which update the present post but I don`t create a new one, I don't know why ?

protected function methodNotAllowed(array $others)
    {
        throw new MethodNotAllowedHttpException($others);
    }

via Chebli Mohamed