Security - you have to love it. It keeps you safe and protected as to who has access to your backend services to enable traffic only from specific IPs.
This was known as a "whitelist", however, it is now more commonly referred to in the more neutral and informative term "allow lists".
When such a backend security limitation is enabled - you will need to add the Ultimate IPs to this allow list. These IPs are used by different services of Ultimate that will communicate with your own CRM platforms, so please add all three.
These need to be added on the CRM side, below you will find tutorials on how to do it in different systems.