@CatAF In a search it would be the

appliedtotransaction

but I don’t think you can get that in an invoice, since the relationship is n:n instead of 1:1

Thanks Matt. I confirmed that in a saved search it's {appliedtotransaction.tranid} which works on non-main lines. Will need to do some more research on if it can work on an email template. It is possible this particular template is only used when a batch process that generates a 1:1 ratio is used, but that would be luck.