When using the OfflineDataSync it's currently not possible to add an Input to the TriggerDataSync action. For cases, where you only want to synchronize data for specific record (e.g. an Order with it's orderlines) you cannot send the OrderId along with the TriggerDataSync.

I always need to use a work-around in my OfflineDataSync switch by doing something like: 

A: Substr(SyncUnit,0,11) = "UpdateOrder"  and in the client-action: 

IntegerToIdentifier(TextToInteger((Substr(SyncUnit,11,100))))

in the TriggerOfflineSync I then enter this in the SyncUnit: "UpdateOrder" + OrderId

B: use JSON (de)serialize logic as SyncUnit variable.

It would be way easier if it's possible to add the custom input parameters (e.g. OrderId) to the TriggerSyncAction and use it directly in my OfflineDataSync.