For users to be able to register to an event, it is necessary to set the permissions on who can register. Registration permissions are possible to set in the same way as other permissions in “Settings > 1. Permissions”. The default permissions are valid for all the events there.
Additionally, it is possible to adjust the permissions which are valid only for a single event. To adjust settings for a single event it is necessary to turn on the option “Permissions per article” and choose a role or add users who have the right to register. Permissions per article overwrite the permissions set in “Settings > 1. Permissions”.