'hedonist, listen to this advice. It's dead right. You aren't going to collect this invoice in time to solve your pressing needs. So play the long game that

'hedonist, listen to this advice. It's dead right. You aren't going to collect this invoice in time to solve your pressing needs. So play the long game that 'tpacek suggests. My suggestions were made on the assumption that your client is a smaller outfit where the nonpayment is due to, well, a desire to not pay you if they can get away with it. If you're dealing with BigCo your invoice might be in payables hell. Endless followup is sometimes required. I get banks as clients. Sometimes they're fast. Sometimes they're ridiculously slow in paying.