Reading the docs here: 

https://www.zabbix.com/documentation/4.2/manual/installation/install_from_packages/rhel_centos

For RHEL 7:
rpm -Uvh https://repo.zabbix.com/zabbix/4.2/rhel/7/x86_64/zabbix-release-4.2-1.el7.noarch.rpm
It's good, but in zabbix repo (after this command):

baseurl=http://repo.zabbix.com/zabbix/4.0/rhel/7/$basearch/

Version 4.2 != 4.0 in repo.