Refer to the exhibit.

To clear the fault raised by the Cisco APIC when the EPG must accept endpoints from a VMM domain, the EPG should be associated with the VMM domain. This association is necessary for the APIC to recognize the endpoints within the VMM domain as part of the EPG. Without this association, the APIC cannot apply the policies defined in the EPG to the endpoints, which can result in errors1.

References :=

APIC Policy Deployment and Resolution Immediacy For AVS VMM Domain - Cisco Community