I am using Azure Maps and when I give it a P.O. Box, it tells me it cannot provide a longitude & latitude for it. I need this for find stuff within a rough distance and so I'd prefer the lat/long of the actual post office, but anything in the area would work.
How can I accomplish this?
US PO Boxes are not generally geocodable. At best, if you have the address the PO Box is located at, you can put that address in. This is not an Azure Maps specific limitation but a general limitation. There are a lot of funky things that go on with PO Boxes (they can be moved to other addresses).