Sending a bill to the wrong person can push payment off as much as 30 or 60 days as it gets routed around a company.  Talk directly with your client and ask who should receive your bill if the bill is going to someone other than your day-to-day contact, call and introduce yourself before you put the bill in the mail.  If you’re sending a bill to your client’s bookkeeper or accounting department, copy your client as well and follow with a phone call.