When an order is put in status 'Paid' (it must have a status code of 'paid' which is the one by default) the module checks the product sales elements stock, if he is no longer in stock it checks for other variations of the product and sets the first one in stock as the default one.

Installation

Manually

Copy the module into <thelia_root>/local/modules/ directory and be sure that the name of the module is AvailableDefaultProduct.
Activate it in your thelia administration panel

Composer

Add it in your main thelia composer.json file

composer require thelia/available-default-product-module:~2.0.0