Currently it is not possible to send emails with unique join code details via Brella. They must be sent manually or through your email marketing software.
To easily send unique join codes through your email marketing software, we suggest to export the invites file from the Admin Panel (manager.brella.io), edit the file to match your email marketing software, and upload it there to send out the emails. As an example of how you can edit the file, Mailchimp allows to use the merge tags (i.e. tagging a column in a certain way to export the data from e.g. unique join code and email columns and send the emails to your attendees with the corresponding unique join codes; read more here).
We are working hard on improving the experience of using this feature. If you have any feedback, please let us know at firstname.lastname@example.org.