SendUserVerificationEmail.php

<?php
namespace App\Mail;

use Illuminate\Bus\Queueable;
use Illuminate\Mail\Mailable;
use Illuminate\Queue\SerializesModels;
use Illuminate\Contracts\Queue\ShouldQueue;

class SendUserVerificationEmail extends Mailable implements ShouldQueue
{
    use Queueable, SerializesModels;

    /**
     * Create a new message instance.
     *
     * @return void
     */

    public $slot;

    public function __construct($slot)
    {
        $this->slot = $slot;
    }

    /**
     * Build the message.
     *
     * @return $this
     */
    public function build()
    {
        return $this->markdown('mail.users.verify')->subject('ProjekIOT @ Email Verification')->with(['slot' => $this->slot]);
    }
}