Meta Box Relationships Custom Fields

Hello,

I have one post type, (offer), that is associated to another post type, (listing), using Meta Box – Relationships. We can have multiple offers associated to a single listing using the Relationships. When working on a Notification that has a trigger for when a offer is added I need to iterate through the Meta Box Relationships, (there should only be one set), to be able to find the associated listing post type and pull the email address from a custom field.

Is there a way to extend and customize the Pipeline with functionality so that I’m able to work with Meta Box Relationships? We have the Custom Field extension installed as well.

https://docs.bracketspace.com/notification/extensions/custom-fields/custom-fields#examples

Then I could use something like this to pull the email address field from the listing:

{postmeta {offer_ID} [meta box relationship(listing_id)]|postmeta,email_address,true}