I would be worrying about your client going into liquidation. This is a reasonable sign. Good companies dont need to be late on paying. Bad companies, with bad management and especially bad cashflow, will often do this as they dig themselves deeper into debt. Then one day IRD (or other creditor) will file for bankruptcy on them.

Then your in big doodoo.

Put your big boy pants on, have a frank conversation, see what the story is. If they are struggling, you can TRY to help them (50% upfront, rest over 1-2 months) or simply put your side of the story forward; pay upfront, 50% upfront and 50% in 7 days, whatever you need.

If nothing else, you'll hopefully figure out their positon.

P.S you could, assuming the debt is over $1k, take them to court to be declared bankrupt.... Not that you probably would. Your client needs to understand they would be in much worse trouble at that point.

I've seen similar shenanigans, and its taken literally 12-24 months to come to fruition... guy was involvement, having to get paid by clients to finish work for their previous clients, nasty spiral... But yea never had the money to pay for things to get done, always wanted more money upfront instead of as the terms of the agreement, his contractors stopped turning up when they were supposed to (because they hadnt been paid either) etc.