How to record vendor invoice for both a purchase order and a project line

We have received a vendor invoice containing both the content of a purchase order (item lines) and an order for a project (an expense without item).

We have recorded the vendor invoice in the invoice register and open it in the invoice approval journal. Here we select Functions - Purchase order and select the purchase order. Normally we would post the invoice in this window but the total does not match so this is not possible. When we book project invoices we select Account type "Project" and apply the project number and category.

How do we connect both the purchase order and the project line to the same vendor invoice?