413 errors occur when the request body is larger than the server is configured to allow. Here’s how you can fix it, depending on your web server:
Apache: Set the LimitRequestBody directive in either your httpd.conf file or a local .htaccess file.
Nginx: Set the client_max_body_size directive in nginx.conf
IIS: Set the uploadreadaheadsize config setting
As you said you checked you PHP ini file so I gues then that upload_max_filesize and post_max_size settings in php.ini is high enough.