It is possible to create an item to calculate vacation provisions for the voucher
It is enough to have an item simply typed Provision for holidays.
However, there are two possible scenarios.
Case 1: Vacation time granted as a percentage of salary. (See here)
In this case, the calculation of the vacation provision will be automatic and the program will recover the entitlement of the month of the employees concerned.
As far as the voucher is concerned, it will suffice to correctly set up the provision account and the corresponding expense account so that the provision and vacation payment items balance out over time.
Case 2: Holidays in days or hours
In this case the program cannot calculate a provision by itself and a fixed monthly amount will have to be entered manually.
On the other hand, as the salary is not differentiated when people go on vacation, it will not be possible to automatically dissolve the provision via the program. In this case, you would have to add items and manually dissolve the vacation when people take it.