The Retailer API (and the Seller Dashboard) is currently experiencing an outage on billing details with regards to the Orders API. We are aware and working on the problem, and we will alert you as soon as we are back online. If any users are in the process of importing their orders, they should stop and re-import them once the issue is resolved.
[RESOLVED] The outage which we reported a short time ago on billing details in the Orders API has been resolved. You can continue your normal business activities and re-import your orders if necessary.