Method FIELDSELECTION_ITEM of BADI ME_PROCESS_PO_CUST not triggering

We have implemented BADI ME_PROCESS_PO_CUST especially on method FIELDSELECTION_ITEM, I look at the sample code and apply almost the same logic in our implementation of this badi. We implemented FIELDSELECTION_ITEM method, however, no matter what breakpoint I put on this method, the debugger does not stop.

In some methods such as OPEN, PROCESS_ITEM, PROCESS_HEADER, etc, they are all ok, i.e., it stop at the breakpoint.

Looks like this method is not being triggered. My question is at what point is this method being triggered?

Anything we missed here? Or any prerequisite I need to do before.