How to use SORTUP funciton in IBM ITX?

Question

I would use SORTUP like this:

=SORTUP(FF1(Mission:In1))

Docs is here: https://www.ibm.com/docs/en/ste/10.1.2?topic=functions-sortupby

M201    WARNING:
    Map: NewMap1   Output: Mission:Out1
    Function SORTUP:  Functional maps that return groups or partitioned items must not be used as input to functions.

FF1 method has this output:

[{"mission_name":"Thaicom","manufacturer_count:1,"manufacturers":["A"]},{"mission_name":"Thaicom-2","manufacturer_count:1,"manufacturers":["A","B"]}]

I would pass as argument the manufacturerCount as a second argument, but WebSphere does not accept in any way, why?

=SORTUP(FF1(Mission:In1),manufacturerCount:Mission:In1)

But then it says

')' is expected.

Please look at the setup of my transformation here: