can I create an invoice where the customer has the option to add shipping insurance?
I'd like to create an invoice where the customer has the option to add an Item directly on the invoice, specifically the option to add shipping insurance.
Unfortunately that's not possible with Square Invoices. Any items to be added to an invoice has to be done by you. I suggest using Square Online for what you're trying to accomplish. Create a Shipping Insurance item so the customer will see the open when adding their items to their cart.