trackable one-time invoice QR batches for shops

[brenzi]

One of our acceptance points runs a delivery service where you order through email, phone or an html form and the goods get shipped (with an invoice yet to be paid or upon payment?). Therefore, the generation of the invoice and the payment happen very asynchronously and it is not easy to track which invoice has been paid, especially because many invoices will be of the same amount.

As a simple workaround, we could use our voucher generations script and modify it to also generate invoice QR's for all the voucher QR's. Instead of pure random, it may make sense to index the QR's incrementally

As the invoice QR's are pre-generated in this scenario, they can not state the invoice amount

For each order:

1. use next unused QR pair of invoice and voucher QR
2. send invoice QR to customer
3. take note of accounting invoice number vs. QR index
4. verify payment with the app, scan QR voucher of the corresponding index to see if the payment has been made and the amount is correct and directly reap the voucher to the main account

While nothing prevents to use these invoice/voucher pairs several times, it may be better to ensure single use to avoid confusion