The month is closed, the VAT return is filed, the figures are agreed with your accountant. Three weeks later someone enters a forgotten expense slip from last month — and dates it to the day it actually happened.
It looks like a well-meant correction. The consequence: the VAT of a filed month no longer matches the system. The trial balance you agreed on has changed. Both sides lose time until your accountant tracks the difference down.
A period lock prevents exactly this. When you mark a month as closed, nothing new can be entered into it, and existing records cannot be back-dated into it. The lock is per period, not per account: if April is closed, nothing enters April.
What if a genuinely forgotten document turns up? Bookkeeping has a settled answer and Kumpara follows it: you enter the document in the period you are in. The record is not lost and the expense is still recognised — you simply see, truthfully, which month it was booked in. The past month stays as it was.
You decide who may open a lock. If it is genuinely necessary an authorised user opens the period, makes the correction and closes it again — but not silently: opening and closing are recorded.
A practical suggestion: lock the month on the day you agree the figures with your accountant, not the day the return is filed. The days before that are for corrections; after it, nothing should move.
You collect the reward for this small discipline at year end, when nobody has to hunt for why last month's number changed.