500 Internal Server Error After Adding Subdomain

Hi
I have Problem in titillate subdomain to wordpress
I Add this Line to my wp-config.php

define(‘WP_ALLOW_MULTISITE’, true);
define( ‘MULTISITE’, true );
define( ‘SUBDOMAIN_INSTALL’, true );
$base = ‘/’;
define( ‘DOMAIN_CURRENT_SITE’, ‘alkoonsoft.com’ );
define( ‘PATH_CURRENT_SITE’, ‘/’ );
define( ‘SITE_ID_CURRENT_SITE’, 1 );
define( ‘BLOG_ID_CURRENT_SITE’, 1 );

And edit .htaccess

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]

# uploaded files
RewriteRule ^files/(.+) wp-includes/ms-files.php?file=$1 [L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule . index.php [L]

After finish adding subdomain (mobile.alkoonsoft.com) in wordpress and Cpanel . I got error message when trying access mobile.alkoonsoft.com/wp-admin

Clearly it’s .htaccess file fault I try to delete whole .htaccess contents and keep WordPress code with no hob .