You have a double-NAT config which will make this harder. Basically, you need a way to tell your ISP modem to forward to pfSense, which will then forward again to the device. Unfortunately, most ISP modems do not have any intelligence in them and you will not be able to add or modify their rules. Far better to put the modem in bridge mode so that PfSense gets your WAN address. But even then you're still in private space, so there is yet another level of NATing going on here to get you to the public Internet. With all these levels of NAT, you're going to find it difficult to share anything.