I can't see any subscription events in Klaviyo

After you turn on the Klaviyo integration, you have to trigger all those events for which you want to set up the flow.
For example, the cancellation event can be triggered by cancelling one of the subscriptions in your shop. After you do that, the event will be sent to Klaviyo in a few minutes.
You can then resume this same subscription, create a new subscription in your shop, etc. and these events will all show up in your metrics in Klaviyo a few minutes after they occur ;)