Speaking from my own perspective and not Milestone's, point of sales integration is a pain. The market is so fragmented, product/feature documentation is extremely difficult if not impossible to find, and some of the POS vendors I've tried to reach out to regarding integration capability have been very unresponsive.
It's not necessarily a secure method, but the easiest to integrate method is when you can point the POS software at a specific IP and port, and it just connects to that address and sends receipt data through roughly the same way it is printed on the receipt. Alternatively if the POS software can be programmed to listen for incoming connections on a designated port, then an external application can connect in, and once the connection is established, the data is pushed out to the client. This seems a bit less common than having the POS make outbound connections.
Unfortunately a lot of POS software does not do this, and the "classic" integration method is to insert a pass-through TCP Serial Server device between the POS and the RS232 printer. The serial server just lets the bits pass through, but an external application can connect to the IP of the serial server and the data is sniffed off of the serial bus.
Going the serial route sounds like a ridiculous step backward, but when it works, it's typically rock solid in my experience. And serial printers are still oddly common in retail for some reason. But USB printers are more and more common now and it's a little bit more challenging to go this route with USB.
I'm not terribly familiar with the text inserter / transaction overlay appliances on offer or the best way to integrate it with NUUO, but I feel your pain.
