There are occasions when one needs to flush DNS Cache (such as when you change your DNS provider to third-party such as Cloudflare or Google). It can be done as follows;
In Terminal run
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
you will be prompted for the admin user password, type it.
Note that there won’t be any confirmation when you run this command, that is okay.