Same issue here. I'm on Ubuntu 22.04 with defaults installs of PHP, Curl, etc.
Here is how I used the solution from oliver.burkill but with Apache:
cd /usr/local/etc/
openssl req -newkey rsa:2048 -nodes -keyout reseller.enom.com.key -x509 -days 3650 -out reseller.enom.com.crt
cat reseller.enom.com.crt > reseller.enom.com.pem
cat reseller.enom.com.key >> reseller.enom.com.pem
chmod 640 reseller.enom.com.pem
echo "127.0.0.1 reseller.enom.com" >> /etc/hosts
# /etc/apache2/sites-available/reseller.enom.com.conf
<VirtualHost *:443>
ServerName reseller.enom.com
SSLEngine on
SSLCertificateFile /usr/local/etc/reseller.enom.com.pem
SSLProxyEngine On
ProxyPreserveHost on
ProxyPass / https://98.124.224.15/
ProxyPassReverse / https://98.124.224.15/
</VirtualHost>
a2ensite reseller.enom.com.conf
systemctl reload apache2
Works for me, now WHMCS connects to eNom without error.