With Standing Orders, your chosen bank will make a fixed payment. The amount will be the same each month, while your invoice may vary from month to month depending on the usage. If you apply for a Standing Order with a value of, for example, Afl. 150,- and your invoice that month is Afl. 156,-, only Afl. 150,- will be paid on that invoice.
This will result in an outstanding balance of Afl. 6,- which you will not receive a notification of, and can lead to a penalty fee. Furthermore, if the outstanding balance goes unnoticed and is not paid, your service can be disconnected. This is not the case with Direct Debit.