Adding items to invoice

What’s the best way to add several items to a specific invoice with a specific number?

I have two options - Generate a new invoice and Add an item to an existing invoice. With “Generate new invoice”, it’s clear - I have a form with invoice number, item’s names, payment terms etc.
But with “add an item to an existing invoice”, I’m struggling to figure out how to add items to an invoice with a specific number, keeping the payment terms the same.
What sorts of relations/formulas should I add?

create a inline list with invoices, and allow to edit (if i understand you problem correctly)

not quite - I need to make sure I can add several items (goods) to a specific invoice. Both on the screen and in the sheet.

im having a hard time to understand… you can add or edit anytime… both on screen and sheet

you mean, that you don’t have extra columns or rows to add item? or your invoice is expandable format? in this case you should have each item in the invoice as a separate record with the invoice ID…