Need to subscribe to codeunit 90 "Purch.-Post" - Due to adding new Type in Purchase Line

Hi,
I’m reaching out about the subscription issue in the Purchase Invoice Posting routine. We’ve added a new Type (Deferral) in the Purchase Line.

Now, when Deferral is selected and we move to the /No./ column, we can choose a Deferral No. after extending the Purchase Line (39).
The problem is, I can’t post the invoice because I haven’t subscribed to the posting routine.

I need help with:

  1. Finding the right event to set the posting group. Deferral, which we developed (similar to FA), has its Main Class, sub-class, and a separate table for the posting group.
  2. Locating the event to post data to the Deferral sub ledger.

If you can share me sample code that would be grate.
Thanks for your help!