Error lluminate\Mail\Mailable::send() when I try send email in Laravel

I am beginner in Laravel. I create function for contact form.

I have this code:

public function sendContactForm($request)
    {
        $this->validate($request, [
            'name' => 'required|string',
            'topic' => 'required|string',
            'email' => 'required|email',
            'message' => 'required|string',
            'captcha' => 'required|captcha',
            'acceptReg' => 'required|integer',
        ]);
        $adminEmail = $this->frontendRepository->getSystemAdminEmail();

        $title = $request->input('topic');
        $txt = nl2br($request->input('message'));
        $userName = $request->input('name');
        $email = $request->input('email');
        $ip = $request->getClientIp();
        $dateTime = date('Y-m-d H:i:s');

        $mailTitle = "Masz wiadomość ze strony". env('APP_NAME')."<br/>";
        $message = "
        <b>Dane wiadomości:</b> $dateTime [$ip]<br/>
        <b>Tytuł wiadomości:</b> $title<br/>
        <b>Imię:</b> $userName<br/>
        <b>Adres email:</b> $email<br/>
        <b>Wiadomość:</b> $txt<br/>";

        Mail::to($adminEmail)->send(new ContactMail($message, $mailTitle, $email, $adminEmail));

        die('mail sent!');

    }

ContactMail.php

namespace App\Mail;

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

class ContactMail extends Mailable
{
    use Queueable, SerializesModels;

    public $message;
    public $title;
    public $sender;
    public $adminMail;
    /**
     * Create a new message instance.
     *
     * @return void
     */
    public function __construct(string $message, string $title, string $sender, string $adminMail)
    {
        $this->message = $message;
        $this->title = $title;
        $this->sender = $sender;
        $this->adminMail = $adminMail;
    }

    /**
     * Build the message.
     *
     * @return $this
     */
    public function build()
    {
        //return $this->view('mail.contactform', ['message' => $this->message]);
        return $this->subject($this->title)
                ->from($this->sender)
                ->to($this->adminMail)
                ->replyTo($this->sender)
                ->view('mail.contactform')->send($this->adminMail);
    }

When I run my script I have error:

Argument 1 passed to Illuminate\Mail\Mailable::send() must implement interface Illuminate\Contracts\Mail\Mailer, string given, called in /var/www/vanessa/app/Mail/ContactMail.php on line 43

How can I repair it?

via Chebli Mohamed