If you want to manage negative salaries, i.e. you want them to be carried over to the following month, you need two specific items.
If the data is recent, these items exist as standard in the basic items. If not, they must be created.
The first must be typed "Catching up of negative salaryl":
This is the one that will recover the overpaid salary from the previous month.
The second one must be typed "negative salary to carry forward":
It is the one that will send the overpayment in the following month.
The program will try to recover the amount until it does (even if the employee does not work every month, the amount will carry over)