Order Printer App: Adding a custum number to invoices

Technical Q&A
1

Hello, I am using Order Printer App for invoices and for refunds. I am currently displaying the order number as the invoice number in my invoice template like this:

- Invoice-Nr.
                              {{ order_name }}

I want my refund template to also have a number which should be GS-order_number-1000. I have this code so far:

- Refund-Nr. 
                              {% for transaction in refund_transactions %}
                                GS{{order_number}}-1000
                              {% endfor %}

What I need is for the “-1000” to also be variable. I need the first refund to be GS-order_number-1000, the second GS-order_number-1001, the third GS-order_number-1002, and so on. I am not sure how I can manage to make the “-1000” dynamic. Any ideas??? Thank you!