Thanks for your nice words @Dome and the suggestion. Very happy to hear you like the app!
Unfortunately, even after reading it a few times now, I still didn't understand it (and it's not clear from the title). It would be great if you could follow the suggestions here if you create a new feature request in the future - thanks!
You write "It would be fantastic if a total amount in € could be displayed at the end". At what "end" would you like to see the total amount, and the total amount of what?
Did you already enable the invoice grouping in the app settings, which shows you the total invoice amount for each grouping in the invoice overview list?