If you want the inputs and data to be empty on page load and create an invoice only when you click “send an invoice”, you would need to remove its data source.
Doing this would complicate some of your logic though since you have a dynamic RG for the payment scheduler and list of items. Every time you would add a payment and item, you won’t be able to reference to an invoice since, well, you haven’t created one yet.
You would need to do some workarounds to make the dynamic RG work on a page / group that don’t have a data type. Increasing the number of cells dynamically is the easy part. The tricky part is saving each cell to the DB. You would need to either use plugins like Orchestra or do it natively using @artemzheg’s awesome tip Dynamic row addition in Repeating Group and bulk CRUD of Things using vanilla Bubble
Hope this helps