Your settings determine whether you can add a payment for a past date. If you received a payment but forgot to record it, you can add it later and register it on the invoice with the correct date.
You can also adjust prepayment dates. If your clinic location settings allow it, you can change the date when adding a new prepayment.
You can back-date payments if your settings allow it. You will find these settings in Settings > Clinic Location. For example, Allow setting prepayment date, Earliest possible date for financial events, and Enable automated financial period locking control whether you can add a payment or prepayment for a date other than today. The financial period settings also affect how far back you can back-date a payment.
Note that you need the appropriate user permissions to manage the payment settings and payment dates in the system. It is also always a good idea to check with your accountant or tax advisor about payment handling to ensure you meet all legal requirements.