The log that might be helpful is /var/log/vcac/catalina.out located on the VCAC appliance. Also, you might want to navigate to the VCAC Appliance Management console https://vcac-ip:5480/ and check if VCO is displayed as REGISTERED. It might be that the process is not started. In this case, you might try to restart it with /etc/init.d/vco-server restart
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are you using the default or an external orchestrator server?
Either way, go to Administration->Advanced Services->Server Configuration and "Test Connection" to see if the connection is failing. if it is try the following.
if you are using the default instance i have seen 2 different issues. 1. If your tenant is using a native active directory identity store it could be preventing the native orchestrator instance from starting. or 2. your default orchestrator server is not started (previous post's recommendation)
if you are using an external orchestrator instance, i have observed that you cannot use SSO authentication and need to change it to the basic authentication where you put the DN of the users and groups.