I searched previous posts and the closest to my question is: Updating Lookup Values with the REST API however I am using the cross-domain library and my update query uses ValidateUpdateListItem method. In my query data the body property is something like this:
"{ 'formValues':[" +
"{'FieldName':'CustomerID', 'FieldValue': '" + dataObject.CustomerID + "'}, " +
"{'FieldName':'RelatedForms', 'FieldValue': '" + <?????> + "'}, " +
"{'FieldName':'ItemID', 'FieldValue': '" + dataObject.ItemID + "'}" +
"], 'bNewDocumentUpdate': false }";
In the part I tried something like { "results": [1, 3] }
but doesn't work. Any ideas?