When you create a new item, its integration to the payslip is not automatic, you have to add it.
Open the file FicheDePaie.ffs (or another file specific to you)
Reminder: to see the whole page, double-click in the margin to open the report properties:
While working in the format, give the page a height of 1297 instead of 297. (Don't forget to put back the 297 at the end of the work).
Example: if you want to insert item N° 3465 :
Click in the middle of the line before the one you want to add. You should get 2 red dots on the left, 2 in the middle and 2 on the right.
Right-click on it :
Choose New details band per copy.
Enter the new item. Execute.
The new line is inserted with the same layout as the other.
Reset the page height to 297 and save.