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Create Extended Attributes for Reference Object IDs
For each extended attribute that you configure, create an additional extended attribute in the same product or product classification for the Id field of every unique sObject or custom object referenced in that configuration. For example, if you use the Contact and Group Census Member objects to reference the State and Age fields in the Member product classification, create two more extended attributes in the same classification, one for Contact and one for Group Census Member, to reference their Id fields.

