we issue invoices for works completed and would like to offer the customers an options to complete payment for the invoice online without having to ring us, they would need to enter their invoice amount manual then progress through the cart and pay on card, we don't need an invoice in magento 2 creating just a record of the transaction.
there will be 2 boxes one for them to type their own amount in (from the invoice) and the other a reference number.
The invoice does not relate to any products in the shop.
