Add your live_key and your test_key as you normally would with Mollie. However, you will notice that we now have some additional fields:
You will need to create an App in your Mollie dashboard > developer. There it will ask for the domain and Redirect URL. Simply copy the Redirect URL from the above field and paste it. Once created, the Client ID and Secret will become visible. Now simply copy & paste those to your payment settings in WooCommerce (see above image).