We're changing the fallback behavior when determining the pricing and publishing that applies to a customer in a specific context. Currently, if a country that doesn't belong to a market is passed as a buyer signal, we use the store defaults. For example, the currency used for pricing will be the store's default currency. With this change, the market for the backupRegion will now be used so currency, catalogs, and other settings from that market will be used when determining pricing and publishing. This fallback matches the behavior on the storefont and allows for consistency in pricing and publishing APIs.
This is a companion discussion topic for the original entry at https://shopify.dev/changelog/contextual-pricing-and-publishing-apis-use-backup-region-fallback