If you have recently applied Curl update and upgraded it to cURL 7.67.0 version, you may receive the following error in WHMCS while access Enom or other registrar domains:

CURL Error: 56 - OpenSSL SSL_read: Success

This is not related to WHMCS or Enom / other registrar issue. This is due to CURL issue. On cPanel server, you can downgrade CURL version to previous version using the following command:

yum downgrade ea-libcurl ea-libcurl-devel

Once it is downgraded, you will need to restart Apache or other web server. If you are using Apache-fpm, lightspeed, nginx etc., make sure that you restart those services as well. Once CURL is downgraded and web server is restarted, it should fix the issue.