With the first programmed key, turn the ignition on for more than 3 seconds but less than 10 seconds. Turn the key off and insert your second programmed key into the ignition and turn the key on within  10 seconds of removing the first key. Leave the second key on for atleast three seconds but no more than 10 seconds before turning the ignition off and removing the key.

 I think that only works if the instrument panel PID "SPAREKEY" reads enabled.  It usually is set to enabled from the factory.

 I know Snap On and Auto Enginuity both have PATS functions. If it were me, I may try manually selecting a 2014 Mustang and try the PATS function. I bet it will work.

I could be wrong , but thought for the last few years of PATS systems Ford started some Bull sh@t where some sort of Incode /Outcode be entered and  do it through a purchased Ford Subscription and have a registered locksmith ID to enter on the site to get those codes you need to enter for the vehicle.

   usa's  ford don't use in code out code, only mazda does and Europe's ford. most of our ford here in usa uses timed pats system, however some new ford vehicles after 2013 uses coded pats system such as 2014 and up ford fusion, some focus maybe 15 and up, ford transit 2014 and up also. there are others but cant remember of hand, done a couple  of this vehicles . what happens here is when you try doing a parameter reset  the ids automatically goes on line and ask for the locksmith or nastf  id and password, once verified it completes the parameter reset. in other words 2 licenses are needed to start this vehicles, the ford ids or fmp  and locksmith or nastaf. hopefully ford don't decide to implement this bullshit on all their vehicles anytime soon.  

   

all you need is a passtru, a windows laptop,  ford j2534 software (fmp) and a 35 dollar sub for 3 days. you can flash/program and do timed pats until your heart is content. I use ford ids 99% of the time but fmp and autel's maxiflash pro works excellent as well.  one question I have though, does your maxisys have the pats function for this model year and if it does was the enable sparekey function available? re enter pats function and after security has been granted there will be a few functions available, enable sparekey should be one of them, if not it needs to be reported.

one more thing, did you register and updated your tool? you stated you took it out of the box and connected to the vehicle.