How to process PO matched Invoice when the UOM on both the documents do not match?

Summary: The Purchase Orders are raised in the primary UOM of the item and received in the same UOM. However, the supplier sends invoice in higher UOM. Customer wants to process these invoices through IDR (Intelligent Document Recognition) but the validation fails as the UOM does not match the PO.

We have set the Item specific Interclass conversion between the 2 UOMs in discussion but the customer wants to raise order in the primary UOM (Ex., Carton) and process invoice in the converted UOM (Ex., KG). We have set the BPA line price in the converted/supplier UOM i.e. KG so that the order quantities are converted when BPA is referenced on the PO but the customer wants to price it based on the primary UOM i.e. Carton.