The service has been set up as ‘private’, restricted to University IP addresses only. This is because if it was opened up to all IP addresses it would create an unsustainable burden on the server, the support staff, pose extra security risks, but also mean that unwanted participants could join rehearsals.
If a non-University member (e.g. part of a University-led orchestra for example) wishes to be part of a rehearsals they will need access to the University network by either: a) coming on site to a college or department space (with suitable agreement); b) being located in a place off-site where there is access via VPN (e.g. a shared household with a University member participating in the rehearsal).