Hey @Valueweb,
Because you said disabling Mod Security causes the error, please re-enable it but this time ask your web host to whitelist the cornerstone-endpoint
directory. It’s only your web host that can fix that since they are the ones controlling the server. Our products are working fine on most web hosts so your current web host might not be using or conforming to WordPress standards.
We’ll continue checking once we can log in.
Thanks.