Hi Manuel,
I’m sorry, but I cannot issue the refund myself, as the app stores do not provide developers with that option. All functional features of SubTotal can be tested before purchasing the Pro version.
As mentioned, the service date can currently be added manually to PDF invoices and is available as a dedicated field for e-invoices. You’re welcome to contribute to one of the linked feature discussions with your specific requirements or ideas. The main challenge is finding a clean UI that supports a single service date, a service period, or no separate date at all. Perhaps together we can find a good solution that can then be implemented.