In Azure AD B2B bulk invitations, the portal and CSV workflow require two core fields: the external user's email address and the Invite Redirect URL that determines where the guest is sent to redeem the invitation.
The study guide notes that the bulk invite template "must include the guest's email address" and that
"InviteRedirectUrl is required to define the post-invite redemption target (such as MyApps or a specific app)." Usernames and passwords are not supplied for B2B guests because "guest accounts authenticate with their home identity provider," and there is no shared key involved in the invitation. Therefore, the only mandatory parameters to successfully process a bulk B2B invite are the email address of each guest and the redirection URL used during invitation redemption.