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:
When 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 the 3465 item :
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.
Give the new item number and click on execute.
Reset the page height to 297 and save.