Workflow Action - Parameters - Field - only listing some custom transaction body fields

Under Workflow Action, under Parameters section, the Field listing shows some, but not all, custom transaction body fields.  If a custom transaction body field is missing from this Field listing, how can it be edited so that it shows on this listing?  Missing one happens to be a Currency Type custom transaction body field.  By the way, under the Condition section of Workflow Action, with Visual Builder, some custom transaction body fields are also not available in the Field column in the Workflow Condition setup.  However, it can be found if the proper Record is selected, so it's unfortunate under