I do not have a good example for that. We usually use an AccessControl to view one invoice at a time, and then put a browse on it for the line items. (Like in the Master-Detail example in the help.)
I don’t think linkField will work with two browses.
You should be able to handle List_Selection events from the invoice browse and then SetQuery on the invoice lines browse.
I’m glad to hear you are enjoying Suneido