FMS in Marketing documents (UDF in Header level) is not getting updated

Hello experts

I am trying to create a FMS in a Marketing document with a SUM query. That would be the query:

SELECT SUM(T0.[LineTotal]) FROM POR1 T0 WHERE T0.[Project]=$[OPRJ.PrjCode.0]

My intention is that when creating a PO and selecting a concrete project, this UDF gets updated with the total amount that has been charged to the project to date. I have activated flag "Auto Refresh When Field Changes" and tried with a bunch of fields, but the field does not get updated and when I click on the magnifying glasses system displays an internal error.

Regards