Blocking All IPs except for Cloudflare IPs

its maybe a dumb question because its already answered in the wiki (if its not outdated)
how can i block every ip except for cloudflare ips?

i know its controlled via access control in server configuration tab but
whats the correct setup because i found different explanations
im running the latest stable openlitespeed

i tried to whitelist the cloudlfare ips in allowed and in deny "all" which returned a 520 error

also is comma seperated needed and a trailing T?

would be grateful for some help