IF in DAX Studio

Hi, I cant share the data but this the code I have

In bold is the part that I am trying to add, above is the suggestion you made 

EVALUATE
    ADDCOLUMNS (
        SUMMARIZE (
            VALIDATED_PD,
            VALIDATED_PD[m_Group_Currency_Amount],
            VALIDATED_PD[d_Customer_Name]
        ),
        "Total Overdue", [a_TotalOverdue],
        "Customer Name",
            VAR f_GM_CustomerPD = VALIDATED_PD[d_Customer_Name]
            RETURN
                IF ( f_GM_CustomerPD = "GM", "GM", VALIDATED_PD[d_Customer_Name] ),
        "Customer Number",
            VAR f_GM_CustomerPD = VALIDATED_PD[d_Customer_Name]
            VAR f_GM_CustomerNumber = VALIDATED_PD[m_Customer_Number]
            RETURN
                IF ( f_GM_CustomerPD = "GM", BLANK(), f_GM_CustomerNumber )       
    )

And this the error: