6.3 PaymentDetailsUpdate dictionary
https://www.w3.org/TR/2020/CR-payment-request-20201203/#paymentdetailsupdate-dictionary

error member
A human-readable string that explains why goods cannot be shipped to the chosen shipping address, or any other reason why no shipping options are available. When the payment request is updated using updateWith(), the PaymentDetailsUpdate can contain a message in the error member that will be displayed to the user if the PaymentDetailsUpdate indicates that there are no valid shippingOptions (and the PaymentRequest was constructed with the requestShipping option set to true).

There appears to be no language/direction metadata associated with this error message, nor a way to localize the message.

(also found in various places in the spec wherever DOMString error appears, for example here)

This is a specific example of (and thus related to) #946 and #948