Step 0 is to formally demand the money, either by issuing them an invoice (if that was your normal practice) or a written demand letter. Email should suffice a

Step 0 is to formally demand the money, either by issuing them an invoice (if that was your normal practice) or a written demand letter. Email should suffice at this stage. Odds are strongly in your favor that they'll simply pay, perhaps after taking a bit of time. Escalation options abound if they refuse to pay.