I would highly suggest to open a ticket on the support website here Centreon (i’m not sure anyone can help with your problem here)

also “this site can’t be reached” is a chrome message, not a server error, your browser can’t find the url or the ip address does not answer in a timely fashion (is your apache/httpd daemon running?),

yes

but i think i have wrong configuration of snmp V3 in linux i wish can u share me the good configuration