beehiiv works in both directions in WP Sync core, and a few options on the beehiiv destination are worth knowing.
Know where every subscriber came from:
On a beehiiv destination, map utm_source, utm_medium or utm_campaign as custom fields and the value lands in beehiiv's own tracking fields, ready to segment on. The referring_site field is passed on the same way. This is ideal when one list is fed by an ad and by your website and you want to tell them apart.
Let beehiiv welcome new subscribers:
A beehiiv destination has a tick box labelled Let beehiiv send its Welcome Email to contacts added by this sync. It is off by default, so catching up an existing list never emails people who joined long ago. Turn it on for new sign ups, such as a lead ad, where a welcome is exactly what the person expects. A Backfill never sends the welcome email either way.
Details stay fresh:
When someone comes through a sync again, their beehiiv fields are updated with the latest values instead of staying as they were on day one.
Reacting to beehiiv events:
The built in beehiiv connection reads your subscriber list. The Connect Pack adds a separate Beehiiv Events card that reacts to what beehiiv itself reports. A bridge can start when a post is sent, when a subscriber confirms, is created or is removed, or when a subscriber upgrades to paid or downgrades to free. WP Sync creates the webhook in beehiiv for you when you connect and removes it when you disconnect, so there is nothing to paste. Your existing beehiiv bridges are not affected, because Events is its own card.