Help needed! Out of the Box Mapping Tool - Using segmentMembership.ups

Hi ​@SarahWa16 
Its depends on the destination type. segmentMembership.ups is a system-maintained profile map: ups is the namespace, each child key is a segment ID, and the membership entry can contain fields such as status and lastQualificationTime. It is not a general-purpose calculated field by itself.https://experienceleague.adobe.com/en/docs/experience-platform/xdm/field-groups/profile/segmentation

For file-based destinations: I would not rely on a master/union audience export containing the membership status of its component audiences if those audiences are not activated. File exports are organized per audience, and the batch mapping reference describes mapping the status path for a particular segment ID. If you need a dependable derived value in the master audience's file, the safer approach is to create and populate it as a regular profile attribute upstream, then map that attribute. Activating the other audiences is another option, but it means activating them—not just referencing them in the mapping https://experienceleague.adobe.com/en/docs/experience-platform/destinations/how-destinations-work/profile-export-behavior https://experienceleague.adobe.com/en/docs/experience-platform/destinations/ui/activate/activate-batch-profile/batch-destinations-mapping-reference

For some streaming destinations, behavior differs. For example, the HTTP API destination can include memberships for unmapped audiences when Include mapped audiences only is off, provided those audiences share the mapped audience's merge policy. If that option is on, only mapped audiences are included. However, the export is triggered by changes to mapped audiences or mapped attributes; a change only to an unmapped audience may not trigger an export. So this can't be treated as a reliable cross-destination solution for a calculated field. https://experienceleague.adobe.com/en/docs/experience-platform/destinations/catalog/streaming/http-destination https://experienceleague.adobe.com/en/docs/experience-platform/destinations/how-destinations-work/profile-export-behavior

In short: if this is file-based activation, materialize the derived value as a profile attribute before activation. If it is streaming, check the connector's membership settings, merge policy, and export triggers first. Which destination connector are you using?