All of my contacts have a studio-created field called "Cust No.".

I was easily able to display this field on Sales Orders by creating a related field:

        Customer -> Cust No.  (selection path)

        partner_id.x_studio_cust_no  (technical name of related field)

However, all similar attempts to display this field as a related field on Invoices have failed.  The most basic method that I assumed would work was:

        Partner -> Cust No.  (selection path)

        partner_id.x_studio_cust_no   (technical name of related field)

I have tried many different paths toward "Cust No." field including through delivery address, company, contact, transactions, etc.  Nothing has worked.

Any help would be greatly appreciated.