How to setup invoice approval based on PO Line Category?

Summary:

We have a requirement to add a BPM rule for AP Invoices which based on the category of the matched PO Line. For example if category code on the PO Line is "78140000-Transport Services" then approval should be sent to person XYZ.

I see that in BPM, following 2 attributes are available to fetch and compare PO Line Category but not sure why my rule is not working as expected.
a) Purchase Order Line Category Name Under 'Purchase Order Line Additional Attributes'

b) PurchasingCategoryId under Invoice Line

I have tried above both in my rule but rule is not getting triggered, hence Invoice is not routed to desired approval. While using PurchasingCategoryId, I have also tried .toString() and .toLong() functions but it did not work. Not sure what is missing.