You can make your own custom fields available for reading or writing on your journals, and expose them to the Certinia API and desktop apps
Compatible applications installed on your local computer. for reporting or document input. For example, you can do this in order to populate custom fields when uploading journals using .
You must create an integration rule (Type 1) to expose your custom fields on the journal object. For more information, see What is an Integration Rule?.
Where are my custom fields?
In Lightning Edition, custom fields on the journal header are available for input along with other header fields, provided your administrator has added them to the journal page layout. To make custom fields on journal line items available for input, your administrator must add the custom fields to the field set that matches the tax mode of the journal's owner company: Manage Lines (Combined), Manage Lines (SUT), or Manage Lines (VAT/GST). For more information, see Journal Line Item Field Sets.
In Classic Edition The view of the application that you see when you first install the base managed package., click the 
icon next to the Journal Description field to complete custom fields on the journal header, and click the icon on the journal line to complete custom fields on the journal line.
In Extended Edition The view of the application that you see when you install one of the extension packages (such as the Cash Entry Extension package). For invoices, credit notes, and journals Extended Edition is integrated into the main package, but must be configured., custom fields on the journal header are available for input along with other header fields. To make custom fields on journal line items available for input, your administrator must add the custom fields to the Manage Lines field set. For information about the field sets on the Journal Line Item object, see Journal Line Item Field Sets.
When using custom input forms, your administrator must add any custom fields for both journal header and lines to the appropriate input forms.