我想发送一封电子邮件给用户，消息如下：
MessageController.php:

public function store(Request $request)
{
    $user_id = auth()->user()->id;

    $message = new Message;
    $message->title = $request->title; 
    $message->body = $request->body; 
    $message->offer_id = $request->offer_id; 
    $message->user_id = $user_id; 
    $message->with_profile = $request->employeeProfile;
    $message->save();
    //return response()->json($message); -> this gives correct message

    $offer = Offer::where('id', '=', $request->offer_id)->first();
    //here I'm trying to get user Id, basing on offer (I knot I should use other way, but I'll correct it later
    $user = User::where('id', '=', $offer->user_id)->first();

    $user->notify(new OfferMessage($message)); -> this gives error "Undefined variable: message" 

    return response()->json(['created' => true], 201);
}

问题是它给了我一个错误："未定义的变量：消息"，当我收到正确的消息时，当我不评论"返回响应（）-〉json（$message）;"
我到底做错了什么？
编辑：
我的邮件类：（我没有OfferMessage类）

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

use Illuminate\Notifications\Notifiable;
use App\Notifications\OfferMessage;

class Message extends Model
{
    use Notifiable;
}

编辑2：通知/报价信息. php

<?php

namespace App\Notifications;

use Illuminate\Bus\Queueable;
use Illuminate\Notifications\Notification;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Notifications\Messages\MailMessage;

use App\Message;

class OfferMessage extends Notification
{
    use Queueable;
        public $message;
    /**
     * Create a new notification instance.
     *
     * @return void
     */
    public function __construct(Message $message)
    {
        $this->message = $message;
    }

    /**
     * Get the notification's delivery channels.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function via($notifiable)
    {
        return ['mail'];
    }

    /**
     * Get the mail representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return \Illuminate\Notifications\Messages\MailMessage
     */
    public function toMail($notifiable)
    {
        return (new MailMessage)
                    ->line('You've got new message: '.$message->offer_id)
                    ->line($message->title)
                    ->line($message->body)
                    ->line('Sent by:'.$message->user_id)
                    ->line('Thank you for using our application!');
    }

    /**
     * Get the array representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function toArray($notifiable)
    {
        return [
            //
        ];
    }
}