Hi @Jakub,
For these scenarios, we typically build a Segment Triggered Flow, and create the required transactional message. Then we contact Klaviyo Support to review the message, approve it as a Transactional message, and then backpopulate the Flow to start sending.
Segments can include unsuppressed people, but until a message is approve for transactional messages, they are automatically prevented from sending to suppressed people.
Some more documentations for others about Transactional messages in Klaviyo that might be helpful:
I’m not sure if you can get Campaigns approved for Transactional Messages, but I imagine someone else here might be able to chime in if they have done that?