FTP Error

I am trying to do a Nougat update for the Zebra TC56 device and when I begin the stage I get the following error:

Query Error, Reason-FMC Couldn't connect to server = [IP Address we set the FTP up on] and port = 21 , check wifi connection.FMC downloadFTPFile Connection is not open.

The TC56 is using Cellular, and the computer we set up the FTP server on is on a wifi hotspot, not the same one on the error message.

What is the cause of this problem, and what solutions are there?

Thanks