Hello everyone I need to create a custom field in item fulfillment to select partner addresses. In most cases, the partner has more than one address. How can I create a custom field with the partner addresses filtering by the transaction partner?

Not sure I'm entirely following, but I think you'd have to create custom address fields (Other Record Field) to tag the desired address for selection or use existing ones like default billing/default shipping.

You need to designate a trigger to tell the system which partner address to pull. how do you determine which partner address to pick today?

The partner inserted in the field partner(id partner) in the item fulfillment.