@nicoonline please try this commands
yum clean all yum -y install yum-utils yum-config-manager --add-repo http://rpm.kamailio.org/centos/kamailio.repo yum install --disablerepo=kamailio --enablerepo=kamailio-5.2.7 kamailio
For `5.3` branch please wait `5.3.5` release. For proper packaging on `CentOS 6` required commit [fc28a14](https://github.com/kamailio/kamailio/commit/fc28a14203f59c62d2c745ffd294a509...)
Not working anymore. 5.2.7 rep not found.