NXT event guest export

For GiveCampus integrations and API.

When event export is enabled, eligible completed registrations export to the mapped NXT event. The registrant/host must resolve to one NXT constituent before the host participant can be created; no match or multiple matches require correction. Other eligible attendees are then exported as guest participants linked to that host, with RSVP/check-in data and a constituent ID where available. This does not promise a new standalone NXT constituent for every guest. Inspect registration export status and resolve matching/export errors before creating duplicate records manually.