My organization contacts can sometimes share the same email address but I have one custom field that is unique to each organization (registration number) and I want to add this custom field to enhance the unsupervised rule. The thing is that I don't see this option. I can use any standard field (city, zip code...) but none of my custom fields appear.
Is this possible and how? Do I need and extension to do so or to set a parameter somewhere?
EDIT 1 : I use CiviCRM 5.25 on Drupal 7.72