The support for dashes is live in the sense that where they’ve been used previously, we’ll continue to support them. When you create a new invoice, it should pick up from your last invoice. If this includes dashes, it should save all OK.
The way I got it to work (I think I was directed to this method via a PM from support) was to copy the desired invoice number from somewhere else (Excel / Notepad / whatever) and paste it into the invoice number field. That worked for me, and now if I create a new invoice the same number convention, including dashes, appears by default and I can just change the numbers as required.
@Michel Agreed! I’m just glad there is a way to get it to work. It’s a pretty small matter in the grand scheme of things, but it might have been a deal-breaker for me if I was forced to use a new invoice numbering system.