Cannot POST api/system/sessions of Graylog2 on CentOS 7

I have an working installation of Graylog 2.1 on Debian 8, but I had to install Graylog on CentOS 7 because my datacenter uses this distribution and I want to have same environment to avoid problems when I need to ask changes in production.

I follow guideline of Graylog for CentOS 7 available in http://ift.tt/2fq7fy0 and installed Graylog 2.1.2. MongoDB, ElasticSearch e Graylog are running and answer to local requests via terminal. However, web interface is not available. Login page is presented, but when I try to connect using admin user, I receive this answer:

Error - the server returned: 404 - cannot POST http://mydomain:9000/api/system/sessions (404)

Below are lines that I changed into server.conf of Graylog (I replaced real IP address here):

rest_listen_url = http://4.8.15.16:9000/api/
rest_transport_uri = http://4.8.15.16:9000
web_listen_uri = http://4.8.15.16:9000/

I have searched for references about this fail and created a graylog-settings.json file based on suggestion of Graylog github issues, with this content:

"custom_attributes": {
    "graylog-server": {
      "rest_transport_url": false
    }
}

But event after restarting server, the problem continues. Graylog log only shows INFO records, then it seems to me that requests are not reaching server. I would like to know if this is due to network configuration or can be solved by an adjustment of Graylog.