Glad that there is progress!

From the File / Specifications screen, can you confirm which advice section(s) are selected to print? You could choose Advice 1 twice, or each of Advice 1 and Advice 2, or Advice 2 twice. If you happened to pick the same Advice twice, then any changes you made to the 'other advice' sections on the spec would have no influence when printing, as they have not been chosen to print.

Or if you have chosen both Advice 1 and 2 to print, ensure that the desired fields/labels exist in the respective 'advice 2' header, detail or footer sections. In this case, you can manipulate all fields/labels independantly.

For dividing vertical lines, you should insert them so that the top of each line is in the detail section, and then format to 'fit to section' as you indicated. The location of the top of the line indicates what section it 'belongs' to. If the top exists in an advice header section and you 'fit to section', indeed it will fit to that section.

If your spec contains two different detail section types (for payments and for cash invoices), you need to insert vertical lines and 'fit to section' for both. Otherwise when you preview within the designer, it will appear as if there are gaps in the detail section of the advice. Printing live checks will choose one detail section or the other (whichever is applicable) and ignore the other.