I am trying to total some columns based on an invoice number, but I can't get
the formula to work.
I have the following columns:
Invoice 1|Amount1|Invoice2|Amount2|Invoice3|Amount3|Invoic e4|Amount4

In another column I have an invoice number. I need the formula to add the
amount if the invoice column just to the left contains that invoice number,
for each column.

For example in A1 is invoice 1234. I need the formula to add all amounts
from Columns Amount1, Amount2, Amount3, Amount4 if the corresponding Invoice
column matches A1.

I tried using the Sumif and Sumproduct, but it is only returning a #VALUE!
error.