How to break up cross-app relationships

Judging from your screenshot of the webhook, it appears that you might have created new fields to hold Record ID#, Record Owner, and Last Modified By (9, 10, and 11). This means we can probably assume that you have changed the Key of the table so that the relationship can work. I think we must also assume that this relationship is not bi-directional as we know from my previous comment that built in fields cannot be overwritten (except by stored imports). If this is the case, what happens when a user needs to add a new parent record before selecting it in the child record? Must they first go to the source app to add the new record and then trigger the webhook? This seems like poor user experience, as the user would have to know that a record must be added to the source app before they create the child record and if they didn't do it in that order, they would need to refresh in order to see the record (created via webhook) show up in the record picker.