There are two things you must do to have a better chance to avoid accepting counterfeit dollar bills:
1: Make sure that your machine is fitted with the latest software upgrade. Older machines or software may not recognize some newer advanced forgeries, i.e those prevalent in Spain now.
2: Always neatly arrange your notes face up (the side with Franklin’s head) and with the head up. Some softwares will not recognize forgeries by looking at the back, or when the portrait is upside down.
Make sure that you neatly arrange your U.S. $100 banknotes and place them in your counting machine facing you.