Nexmo serves the https://rest.nexmo.com and https://api.nexmo.com endpoints via a CDN (Content Delivery Network) provider, as well as directly. The goal of implementing a CDN is to serve content to all Nexmo customers with both high availability and high performance.
Issues will be experienced if you try to reach our services from a static IP address, you will need to use rest/api.nexmo.com. Hence you it is recommended that you do not whitelist outgoing connections to any of our REST API IP addresses on your firewall.
We recommend against storing local copies of these certificates in your platform or application, but they can be found at Certificate for *.nexmo.com.