Swiss QR Bill is not rendering, if invoice nr. have letters

Which version of Invoice Ninja are you running? v5.5.36 Which environment are you using? Shared hosting Have you searched for existing problems/inquiries? yes Additional context For the invoice number, I use a custom number pattern that looks like this: R-{$customer number}{$date:yW}{$counter} My customer number is also letter-based, like ABC-F or ABC-P. So the full invoice number looks like R-ABC-F224301. Since the QR reference number does not contain any letters, the invoice number has to be "translated" so that the QR generator provides a valid reference number. With little effort I was able to solve my problem. I am happy to make this solution available as a PR, as others might also benefit from it and I myself would not have to re-install the manual changes with every update... More about my solution: I read the invoice number into a temporary variable and run it char by char through a loop. If the char is a number, it is taken over unchanged. If the…