Unable to register due to no message error when registering a lavel post

//Create a post
    Route::post('/list/create/contents', 'Board\BoardController@createContents')->name('board.create.contents');

            <form action="{{route('board.create.contents')}}" }" method="post" class="contentsForm">
                <article>
                    <div class="boardContentInfo">
                        <div class="boardWrtTitle">
                            <span>Name</span>
                            <p>{{login()->user()->user_nm}}</p>
                        </div>
                        <div class="boardWrtTitle">
                            <span>Horsehead</span>
                            <select name="category">
                                <option>- Select separation -</option>
                                <option value="Contact Us">Contact Us</option>
                            </select>
                            <div class="QnAWrtEx">
                                <p>This article is written only in secret.</p>
                            </div>
                            <div class="boardWrtTitle">
                                <span>Title</span>
                                <input type="text" name="subject" style="width: 80%;" />
                            </div>
                        </div>
                    </div>
                    <div class="boardContentDetail">
                        <div>
                            <textarea id="contents" name="contents"></textarea>
                        </div>
                    </div>
                </article>
                <input type="submit" value="registration"/>
            </form>

<?php
//Definition of requests received when registering a post
namespace App\Http\Main\Board\Domains\Requests;

use Illuminate\Foundation\Http\FormRequest;

class BoardContentsCreateRequest extends FormRequest {
    public function authorize(){
        return true;
    }

    public function rules(){
        return [
            'writer' => 'required|string',
            'subject' => 'required|string',
            'contents' => 'required|string',
            'category' => 'required|string',
        ];
    }

    public function attributes() {
        return [
            'writer' => 'Author',
            'subject' => 'Title',
            'contents' => 'Content',
            'category' => 'Headlines',
        ];
    }
}

 //Posting Registration Controller
    public function createContents(BoardContentsCreateRequest $request){
        $contents = $this->boardService->CreateContents($request->all());
        returnredirect()->back()->with("alert"",Posting successfully registered.");
    }

//Posting registration service
    public function CreateContents($datas){
        return $contents = BoardContent::create([
            "writer" => Login::user()->user_nm,
            "subject" => $datas["subject"],
            "contents" => $datas["contents"],
            "category" => $datas["category"],
            "reg_dt" => now(),
            "ip"=> request()->ip(),
            "notice_yn" => "0",
            "reg_id" => Login::user()->user_id
        ]);
    }