Multiple Sumifs

[Jackprendergast]

Hi there

I'm having trouble using multiple sumifs. I have sales data in one tab showing customers orders. The data includes customer name, sales value and shipment month. There may be multiple sales for each customer in the same or separate months. In tab 2 I have a summary table showing customers down one side and months along the top. I want to summarise what each customer sold in each month. I've attached a file to this thread (I think) as an example of the information.
Any help would be greatly appreciated!

Many Thanks

Jack