Sync Eventbrite registrations to HubSpot and Mailchimp

Every 15 minutes on a cron, pick up new Eventbrite registrations and mirror them into HubSpot and Mailchimp so the marketing stack is always current. This is a deterministic three-system sync — no drafting or reasoning required, every step is a known operation over structured inputs.

Step 1. From Eventbrite, call List Orders by Organization filtered to orders created since the last run's high-water mark (persist the max `created` timestamp between runs so already-processed orders are skipped). For each order returned, call List Attendees by Order to get each attendee's `profile.email`, `profile.first_name`, `profile.last_name`, and the per-attendee `answers` array for any custom registration questions. Also carry through the event name and the order's `created` timestamp.

Step 2. Push those attendees into HubSpot with Batch Upsert Contacts, matched on `email` as the unique property, in batches of up to 100. For every contact set `firstname`, `lastname`, a custom property `last_eventbrite_event` to the event name, and `last_eventbrite_registered_at` to the order's `created` timestamp. For brand-new contacts also set `lifecyclestage` to `lead`. Contacts that already exist get updated in place — do not create duplicates.

Step 3. Subscribe the same attendees to a configured Mailchimp audience via Add Member. Send `email_address`, `status: "subscribed"`, and merge fields `FNAME` (first name), `LNAME` (last name), and `EVENT` (event name) so the audience can be segmented per event. Treat a 400 response with title `Member Exists` as a success — that just means the person was already on the list.

Configuration the workflow needs: the Eventbrite organization ID, the HubSpot custom property names (`last_eventbrite_event`, `last_eventbrite_registered_at`) which should be pre-created in HubSpot as single-line text and datetime, and the Mailchimp audience (list) ID plus its `FNAME`/`LNAME`/`EVENT` merge tags. Persist the high-water timestamp in the workflow's own storage between runs; on the very first run, seed it to now so history isn't backfilled.

Reference patterns: two of the most-installed Eventbrite Zaps combine Eventbrite → HubSpot (contact create) and Eventbrite → Mailchimp (add subscriber). See https://zapier.com/apps/eventbrite/integrations and https://zapier.com/apps/eventbrite/integrations/google-sheets--mailchimp.