How to enter a deposit in a closed period
A deposit cannot be entered in a closed period. The period would need to be reopened to the month in which the deposit will be entered.
After the period is reopened, you will be able to enter the deposit and re-close the period.
If it is not possible to re-open the period and if permission allows, you could also enter the deposit using a journal entry. However, the transaction would not show on the deposit register.