Before integrating Express button, make sure you’ve covered all necessary prerequisites.
To integrate Express button, you have to be using Klarna payments in your store, either through direct integration, a payment services provider (PSP), or a third-party platform.
Allowlisting (also known as whitelisting) is only required in live (production) environments.
To get any of the identifiers allowlisted, contact your Klarna delivery manager.
The allowlisted domain has to start with https://, for example, https://www.klarna.com.