External reference changing with InputBox - vba

Question

Good morning,
I have two different workbooks (wb1 and wb2), each has two worksheets, "2018" and "2019", containing some data.
I'm trying to create a macro that takes an input with InputBox that has to be 2018 or 2019 and, depending on the choice, it has to insert a SUMIF formula into the worksheet whose name has been tapped in, in the second workbook, with reference to different columns of wb1.
The point is that, depending on what it is inserted in InputBox, the formula in wb2 has to reference to the worksheet "2018" or "2019" of wb1.
=SUMIF('[wb1.xlsm]2018'!$C$3:$C$4412;A3;'[wb1.xlsm]2018'!$K$3:$K$4412)
Above there is the formula that I have now. Is it possible to remove "2018" after the square bracket and add the variable related to InputBox?
Thanks for your help
Edit from comments:
I tried to modify the formula, using Application.SumIf. The problem is that it now gives me run-time error 1004 Application-defined or object-defined error on the line that starts with Sumact = Application...
year_check = InputBox("Insert the year you need to check")
schedule_worksheet = "Schedule - " & year_check
family_worksheet = "Family - " & year_check
Dim Sumact As Range
For i = 9 To 200
index_row = index_row + 1
Set Sumact = wbfu.Worksheets(family_worksheet).Range(Cells(2, index_row), Cells(2, index_row))
Sumact = SumIf(wb.Worksheets(schedule_worksheet).Range("C:C"), wb.Worksheets(schedule_worksheet).Range(Cells(1, index_row), Cells(1, index_row)), wb.Worksheets(schedule_worksheet).Range("K:K"))
Next i