Your reference is MIA
You may provide your future employer with contact information for your professional references, but when he or she reaches out to them, the phone number or e-mail address you provided was incorrect or no longer in service. Or, the reference doesnt respond (perhaps they are of the country on vacation or on maternity leave). What impression does this leave with your prospective employer?
Call or e-mail first to see if they are willing to serve as a reference (if their employer allows it), then get their accurate contact information and check their availability.