Yes, I am running hotspot and user manager on the same router. I have a Level6 RouterOS. The Router Local IP address is 172.16.0.1 amd hotspot IP address is also 172.16.0.1. What is going to be the User Manager IP address?

You need to use 127.0.0.1 for the communication between HotSpot and User Manager installed on the same router,
http://wiki.mikrotik.com/wiki/User_Mana ... ame_router

Hi,
You can Also use WAN IP for the Purpose.