Bad Request: Error occurred in the backing network provider: IPv6 local address [xx:xx:xx:xx] in Local Endpoint=[/infra/tier-1s/<TIER1_ID>/ipsec-vpn-services/<IPSEC_VPN_ID>/local-endpoints/<ID>] is not allowed using deprecated VPN API. The IPv6 IPSec vpn feature is not supported with deprecated API., error code 501917
This is known issue affecting the Cloud Director 10.4.x and 10.5.x releases.
This issue is resolved in VMware Cloud Director 10.5.1.1, available at Downloads.