Dear Yahoo Store Owners:
This is going to be a very important update from the perspective of giving the customers a smooth experience to the store and will end up having all the checkout systems synchronized.
This is what Yahoo! had to say on their official blog.
Before heading into the weekend, we want to remind merchants who’ve recently migrated to Checkout Manager to publish Order Settings before old checkout systems are shut down on SEPTEMBER 1.
If your store was automatically migrated to Checkout Manager after August 15 (this applies to all stores not user-migrated prior to this date), your Order Settings were not published as part of this migration. If you have not published Order Settings since the migration, you must do so before September 1.
If you don’t publish Order Settings, your checkout will no longer function once the old systems are shut down. Your store will not be able to accept any new orders until Order Settings are published.
Stores built in Store Editor will also require an Editor publish for new order button settings to take effect. If your store uses custom order buttons or has any old checkout links hard-coded into the site template (links pointing to order.store.yahoo.com URLs), you’ll need to manually update these links to point to order.store.yahoo.net URLs. Learn how.