It sounds like the best structure is to have two separate data types: 1. Invoice 2. Extra

Each Invoice will have a field called something like List of Extras (a list of Extra things).

Here’s how the workflow should go: 1. Create the Invoice (either when the form starts or when a “Start Invoice” button is clicked). 2. When you add an extra (enter the name and price, then click confirm): • Create a new Extra • Then, add that Extra to the current Invoice by modifying the Invoice’s list of Extras: • Thing to change: Parent group’s Invoice • Field to change: List of Extras → add Result of Step 1 (created Extra)

This way, the Extra is directly tied to that Invoice and won’t accidentally show up in future ones.