[Plugin: RSEvents! – Event Calendar] problem with owner

I cannot see how to set things up so Admins appear as options in the ‘owner’ field of new Events screen…it is just blank…tried setting up a group of wordpress Admins, but no impact. Grateful for any help. Not sure if it is related, but when I try manually to add a subscriber, nothing appears in the ‘username’ box either

https://www.ads-software.com/extend/plugins/rsevents-events-calendar/