Create named ranges : File_Name, Sheet_Name and Column_Name in "Helper"
in "Summary"
in B2
=SUMPRODUCT(SUMIFS(INDIRECT("'[" & File_Name &"]" & Sheet_Name & "'!" & Column_Name &":" & Column_Name),INDIRECT("'[" & File_Name &"]" & Sheet_Name & "'!A:A"),$A2))
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NotE: ALL workbooks must be open.
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