I tried below, which should just return all "Londons" Sales of 18,20,
32 etc etc, but I get a #Value

=SUM(SUMPRODUCT(('Sales Mix'!A:A="London")*('Sales Mix'!
B:B={18,20,32,140,172,208,212,500,99,204,203})*'Sa les Mix'!D:D))



This formula below gives me the correct total sales I'm after in all
Areas

=SUM(SUMIF('Sales Mix'!B:B,
{18,20,32,140,172,208,212,500,99,204,203},'Sales Mix'!D:D))