Only Opal admins can invite teammates to join Opal. There are two ways for a teammate to be invited:
Opal natively integrates with identity providers, such as Okta, Google Groups, LDAP, and Active Directory. If a teammate is added in an identity provider managed group, then they should be added to Opal
You can also scroll down to the bottom of the Opal navigation menu where is says Add Teammates. With this method, you can use individual emails or upload a CSV.