how to handle free giftcard / vouchers

Hi there,

my customer uses managed giftcards. In a couple of cases the following scenario happened:

A customer bought a giftcard e.g. 50€, Code ABC123. Days or weeks later the customer wants to use it for a receipt of 80€. Normaly Giftcard + 30€ cash or card = fine

The Staff uses giftcardpayment and changes the amount to 80€, cco accepts the changed amount. In the used gift Card ABC123 is still 50,-. I tried to reproduce that behavior, the only way I found is to use a free giftcard an set the Numer on ABC123 (what has no influence on the bought giftcard ABC123)

That also works when using the giftcard for a lower amount. GC (BCD234)=50€ receipt = 20. Using a free giftcard and scanning the Barcode in to the Field the cco accepts the payment and BCD234 is still untouched 50,-€

What is the sence of that free giftcard when the shop uses managed ones? The option of making mistakes and to cheat the company is given. How can I disable it?