Creates a pre-population token that allows registrant details to be pre-filled on a registration form. Returns a token and a ready-to-use resume URL.

Pass event_id and any registrant fields (e.g., fields[email], fields[first_name], fields[package_id]) to generate a token. The returned URL (https://client.swoogo.com/event/resume?i=TOKEN) can be sent to the registrant to let them complete registration with their details pre-filled.

Common use case: sending personalized registration links via email campaigns or CRM integrations where you already know some attendee details.