How to assign a "Not validated" invoice to a user using a Routing attribute?

Summary:

To identify an invoice sent thru IDR as Prepayment, we've enabled a Routing Attribute to do this. So, if the email has _PP in it, we want to park it for review. With this, we want to assign the invoice to a user/group of users for checking/update. How do we do that?

Note: The status of the invoice imported in the system is "Not validated".

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