Sort by sum

Hi,

i need to sort the attached Report by sum per customer (3rd group). I inserted a -NL sum function in cell C12 and filtered with this cell in field G12 (Customer No.). It doesn't work! The Report has already a sorting by salesperson (see row 10). What is the reason for the value error in the customer line (row 12)

Thanks.

Kind regards

• CUST003 Sales Amount by Salesperson and Item Type and Customer.xlsx