May Day! Still struggling with this, sorry. When I create an invoice and select marked as paid it insists on a billing address in step 1.
I don't have a billing address because it's a new member who hasn't made a purchase yet. Customer made a theme purchase via an external source, then created a support account on my site and so I need a way to give access to the download for 12 months, after which they can pay to renew or not.
I figured I'd either create an invoice marked as paid, or mark it as paid after generating it, or set the purchase price/invoice value to 0.00 or add a separate credit line for the cost of the item to negate the cost so no payment is attempted.