StageNow Query Error

Hi,

I'm trying to roll back a Zebra TC70 device from Oreo 8.2 to Marshmallow and keep receiving the following error below.

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

I am not sure why this error keeps occurring or how to go about resolving it