When VCSA (vCenter Server Appliance) update failed during a package installation, it is impossible to start/stop VAMI operation. Also rebooting VSCA VM will not solve the issue as vCenter will no longer work.
To solve this, log in to the VCSA appliance via console or SSH and check software_update_state.conf file for pending updates.
Delete the file and VCSA will resume normal operation and the update is ready to be installed.
rm -f /etc/applmgmt/appliance/software_update_state.conf