When I say dummy field, actually, it will be a actual field that should be added to your child post type that should hold the same value that is saved to your parent post custom field.
I understand but there is no other solution available.
If you can share working admin access details and problem URL let me see if I can able to share any other workaround. As the old access details you shared is not working at this end.
*** Please make a FULL BACKUP of your database and website.***
I would also eventually need to request temporary access (WP-Admin) to your site. Preferably to a test site where the problem has been replicated if possible in order to be of better help and check if some configurations might need to be changed.
I have set the next reply to private which means only you and I have access to it.
Can you tell me exactly the name of the method of functions where the custom filters are made, we want to know how to create a new custom filter for the children that is related to the parent (using code).
