I've connected SkySafari 6 Plus (iPad Pro) via wireless to a new SkyFi that is connected to the ETX90 via an AutoStar #497. After the initial set-up with AutoStar including completing an Align operation, I try to issue a GoTo Command, and I get an error in SkySafari:
"Command Failure: The scope can't slew to the target coordinates because they are invalid"
If I select a star and try to go to it, I get the same error. It's also the same if I use the Align function on SkySafari. So basically, it sounds like there is some kind of protocol error between SkySafari and the ETX90.