HiI'm trying to get a list of open invoices with the same PO number. I've got a list of all the invoices but is there an easy way to separate paid from unpaid?

 Hello Accounts-Vlslang, welcome to the Community. To get a list of open invoices you can go to sales>all sales> in the drop down that sales type change it to invoices> you will then see a drop down option that sales all status>change that to open or to paid depending on what you wish to view. Then you can filter by customer/date if you wish.

If you also need to filter by another field the best way to do that is in reports. We just need a bit more information so we can advise the best report to use. Is this PO number something you are manually adding in a custom field box?