The errorCode and errorMessage fields on SubscriptionBillingAttempt are deprecated. These fields were deprecated in version 2025-01 with the introduction of processingError. Developers should now use processingError.code and processingError.message instead. If you haven't updated your code to use these new fields, please do so to ensure compatibility with the latest API version.
This is a companion discussion topic for the original entry at https://shopify.dev/changelog/remove-deprecated-errorcode-and-errormessage-fields-from-subscriptionbillingattempt