If you want to connect your Adyen account for cards payment processing, follow these steps:
In Adyen's sidebar, go to Developers -> API credentials
Click on "create new credential"
Select "Web service user" and click on "Create credential". In the description, please type "Kolleno access".
Safely copy the API key (you will need it later)
Ensure the roles look like this (7/7, 2/2, 5/6):
Click on "Save changes"
Go to the Kolleno app -> Settings -> Payments -> Adyen -> Connect
Enter the Live endpoint prefix you can find in your Adyen account. You can get your live URL prefix from your live Customer Area under Developers > API URLs > Prefix.
Enter your Adyen Merchant Account
Enter the Secret Key (the API key you created and safely copied earlier):
Test the connect and click "Connect"