linkedObjectIds property
linked_object_ids are a list of other objects such as event ticket, loyalty, offer, generic, giftcard, transit and boarding pass that should be automatically attached to this offer object.
If a user had saved this offer, then these linked_object_ids would be automatically pushed to the user's wallet (unless they turned off the setting to receive such linked passes). Make sure that objects present in linked_object_ids are already inserted - if not, calls would fail. Once linked, the linked objects cannot be unlinked. You cannot link objects belonging to another issuer. There is a limit to the number of objects that can be linked to a single object. After the limit is reached, new linked objects in the call will be ignored silently. Object IDs should follow the format issuer ID.identifier where the former is issued by Google and the latter is chosen by you.
Implementation
core.List<core.String>? linkedObjectIds;