HTTPS communication with <TargetAppliance> failed: Peer certificate cannot be authenticated with known CA certificates: Error when using Sophos Firewall appliances

SUMMARY

When adding a Hot Copy Replication target to a source you may get a "HTTPS communication with failed: Peer certificate cannot be authenticated with known CA certificates" error when using Sophos Firewall appliances

ISSUE

When adding a target to a source appliance  if you get the error "HTTPS communication with <TargetAppliance> failed: Peer certificate cannot be authenticated with known CA certificates" and  a Sophos Firewall is in use on the network.

RESOLUTION

You may need to add an exception in the Sophos firewall's Web Proxy service to allow certificate pass-through of certificates other than the firewall's own certificates. Certificate creation and exchange is required for OpenVPN which is used for Hot Copy between Unitrends Appliances.