I am trying to figure out the correct syntax to exclude all invoices when the net amount is $0 due to returns.

I was able to extract the original invoice on the return invoices so that I have the original invoice record for, say $12 then a return invoice now populated in the invoice number field of the original invoice the return is for with a negative $12. So when these are grouped, since it's on the same invoice number now, the net amount of $12 - $12 = $0

Or whichever way to excludes these invoices since they cancel each other out.

They do not want to see these invoices that cancel each other out.