Change WordPress user roles and capabilities › Forums › Restrict or Permit access inside WordPress – how to › Multisite Network – Give users multiple Roles on signup › Reply To: Multisite Network – Give users multiple Roles on signup
Try this variant:
go to Network Admin -> Settings -> User Role Editor -> Default Roles
and select roles, which you which to grant to new user on sign up in addition to a primary default role.
This selection is global for all sites of the multisite network. Take into account that other default roles should exist at the site, in order to be assigned to the new registered users.