Usually the navigation property name does not exactly match its corresponding Smart 3D relationship name. To determine the specific Smart 3D relationship name, look in the Description annotation.
For example, to determine the meaning of the PermissionGroups navigation property on the PermissionGroupFolder entity, view the PermissionGroupFolder/PermissionGroups annotation (shown below) that shows it uses the Smart 3D BelongsToFolder relationship:
<Annotations Target="Com.Ingr.S3dAdmin.V1.PermissionGroupFolder/PermissionGroups">
<Annotation Term="Org.OData.Core.V1.Description" String="Navigation property from the PermissionGroupFolder object to the collection of PermissionGroup using the BelongsToFolder relationship" />
<Annotation Term="Com.Ingr.Core.V1.DisplayName" String="PermissionGroups" />
</Annotations>
Annotations can be accessed at <ServiceRoot>/annotations/$metadata.