The feed was working good and exporting file to server, google fetch correctly. But one day all products was disapproved by google because missing attribute availability. I downloaded feed file and the column availability empty. Not sure when and why it happened.
Seems, this is bug. Tested on demo and not exporting "Availability". Reported to bug tracker.
CS CART team charged me 5 points from my account to get me this answer which I couldn't find in documentation. Sharks!!!!
Unfortunately, at the moment there is no way to configure default CS-Cart/Multi-Vendor to use product stock status as value for the Availability feature automatically. If the product becomes out of stock, the Availability feature should be changed for it manually.
Availability is mandatory by Google. Availability is frequently changing value which is impossible monitor and always change the value. This means you'll get charged per click even product is out of stock.