The 8899 is the Port Number. The IP address of the SkyHunter is 10.10.100.254.
Did you check the iOptron manual? It is explicitly mentioned there (see the very end of the document; but you should read the entire manual if you own this mount).
Use a colon (not a slash) for port number, i.e., 10.10.100.254:8899 if the program does not accept a separate port number. See how you address ports here:
Quote: "An IP address can also include a port number. The port number follows the IP address and is separated by a colon (for example, 250.250.250.1:8451)."
If you are using ASIAIR, the Mount Setting accepts the port number in its own text field, so there is no need to append to the IP address.