For data to flow between CallHub and Luminate Online, you need to whitelist CallHub's IP 188.8.131.52/32 in Luminate Online before integrating it with CallHub. Here's how you can do it in Luminate Online -
Step 1 - Login to your Blackbaud Luminate Online instance.
Step 2 - Navigate to : Setup > Site Options
Step 3 - Here, Select tab "Open API Configuration" and open "Edit server API configuration"
Step 4 - Add a new IP range to your Instance.
Step 5 - Ensure that you click the Save button after adding the IP.