If you go live with Adyen, so not a Sandbox account, you will need to know your "live endpoint prefix".
The live endpoints are set up automatically. To view the structure of your live endpoints, you can refer to our API explorer > select an endpoint > navigate to Going Live. The live endpoint URLs contain a prefix which is unique to your company account. To get your prefix, you need to:
Log in to your live Customer Area.
Go to Developers > API URLs.
On the API URLs page, you can see your unique prefix for the region your are connecting to.
In Kolleno, just enter it in the field "Live endpoint prefix":