cannot send mail using mailgun

I am using mailgun driver in laravel app and tried to send mail. But it gives me this error

Expected response code 250 but got code "530", with message "530 5.7.1 Authentication required

config/mail.php

'driver' => env('mailgun', 'smtp'),
'from' => [
        'address' => env('MAIL_FROM_ADDRESS', 'arshaikh_17@hotmail.com'),
        'name' => env('MAIL_FROM_NAME', 'Example'),
    ],

.env

MAIL_DRIVER=smtp
MAIL_HOST=mailtrap.io
MAIL_PORT=2525
MAIL_USERNAME=null
MAIL_PASSWORD=null
MAIL_ENCRYPTION=null

services.php

'mailgun' => [
        'domain' => env('mydomain.com.pk'),
        'secret' => env('key-********************'),
    ],

What is wrong with my settings and is there anything else you need to check? Please help I have been trying to study laracast for past 2 days but it doesn't send mail.

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