Dhananjay Rau wrote:
The job was so small that I didn't bother to wait for a PO
A PO is simply a specification of the work. It isn't some magic formula for getting paid. I rarely receive them but I'm always paid.
Subsequently, they kept sending me new questions and additional small work with apologies
That's a clear indication that they had not only received the work, but were happy with it.
Do I just forget about it or can I do something about it?
If you haven't yet sent your invoice, do it now. If they come back and say they can't accept it, you can issue a revised one - with the same payment date - to include a PO ref., but if they don't offer one then they must, by law, accept your invoice.
If they fail to pay on time then you'll need to escalate your demand for payment in the usual way (reminders, final demand, etc). Just because it would be uneconomic to take them to court doesn't mean you do nothing, even though you won't want to spend a lot of time on it.
Definitely make use of the Blue Board to warn us of this poor client, but maybe leave it a bit. It's early days. But it would be useful to know if they're well known for trying to get work for free.