When creating a site pair the following error was encountered: Site pairing with HCX manager is not permitted without registering a valid NSX Manager. Register the NSX manager in appliance management interface at the destination HCX manager and retry.
As of HCX version 4.11.x this is now a product requirement for NSX to be registered within the destination environment. Source documentation: https://techdocs.broadcom.com/us/en/vmware-cis/hcx/vmware-hcx/4-11/hcx-4-11-release-notes/vmware-hcx-411-release-notes.html
Usability Enhancements and Changes