You can set a discount code to non-active through the following steps:
1. Go to the main menu and select "Settings", then you click on "Discount codes".
2. Select the discount code you want to stop.
3. Click on "..." next to modify, then you click on "Modify".
4. You can stop this in several ways.
-Change the name.
-Discount back to 0.
-Change the validity to today or yesterday.
Normally the "valid from date" to the past, then the code is immediately no longer valid.
On the reservation form, the inactive discount code will be shown with a red X.