The userId field on a OnboardingMilestone record in Skarn Suite (the platform auth hub: SSO, tenancy, billing, entitlements, internal event bus) stores a specific piece of the data; it is a reference linking this OnboardingMilestone record to the related record it belongs to, so the application can join them and present connected data together. In everyday use this is part of how OnboardingMilestone records are created, displayed, validated, and reported, and it is grounded strictly in the real schema fact OnboardingMilestone.userId: String.
Technical section
Data model, API, and internals — visible to developers.