WHMCS has discovered a problem in an earlier EA4 Curl Package introduced on CentOS servers.

Update!

UPDATE: This is reportedly fixed in ea-libcurl-7.67.0-2.2.1, so it should no longer be necessary to downgrade. (https://github.com/CpanelInc/libcurl/commit/7ca2bbb724ac54a3c41950c8736076953bf1429b)

Working versions:
* ea-libcurl-7.66.0-1.1.2.cpanel.x86_64
* ea-libcurl-7.67.0-2.2.1.cpanel.x86_64
Buggy version:
*ea-libcurl-7.67.0-1.1.2.cpanel.x86_64

Per https://forums.cpanel.net/threads/cpanel-curl-update-breaks-whmcs-enom-module.663449/ it may be necessary to restart PHP-FPM to apply the changes to the running PHP binaries.