JSON_API don't return data on wordpress

Question

I had a problem about wordpress.

I used wordpress 4.5.3 with plugin json-api 1.1.1 and i installed wordpress on ubuntu 16.04, i used apache2 and php7.

When i installed and activated plugin json-api on wordpress. When i clicked link get_recent_posts it returned

The requested URL /api/get_recent_posts/ was not found on this server.
Apache/2.4.18 (Ubuntu) Server at 172.16.1.38 Port 80

This is file config virtual host:

<VirtualHost *:80>
  #ServerName www.example.com
  ServerAdmin webmaster@localhost
  DocumentRoot /var/www/wordpress

  <Directory />
    Options FollowSymLinks
    AllowOverride None
  </Directory>
  <Directory /var/www/wordpress>
    Options Indexes FollowSymLinks MultiViews
    AllowOverride None
    Order allow,deny
    allow from all
  </Directory>
  ErrorLog ${APACHE_LOG_DIR}/error.log
  CustomLog ${APACHE_LOG_DIR}/access.log combined
  #Include conf-available/serve-cgi-bin.conf
</VirtualHost>

I don't know what is problem ? Hope everybody can explained for me, why it don't work ?