I've rebooted the machine, opened the Dynmo software and tried again.
I've even rewritten the instructions ( https://github.com/DoESLiverpool/wiki/wiki/Sticky-Label-printer )
but nothing seems to help
I'm sure there's something obvious, but I can't find it. When we get to it we can put it in the instructions.
Have documented the other label printer in the meantime.
Fixed by plugging the USB in.
First label I printed was "Check USB plugged in if not working"