Exclude customers/orders from the dunning process

To exclude an order from the dunning process, open the order in question, scroll down to the bottom of the Overview tab to the Free text fields section (Freitextfelder) and activate the option Exclude from dunning (Vom Mahnwesen ausschließen) there. 

Alternatively, you can exclude a customer from the dunning process by opening the customer account and activating the field Do not create dunning (Keine Mahnungen erstellen) in the Data tab.