Setting up OneBox-Opencart availability transfer: warehouse+supplier

Good afternoon. If you pass the quantity field to the opencart, then it can be taken by default only from the availability in the warehouse or from the product availability field. If you need to add up the availability of a warehouse and suppliers, you will probably be helped by some action that sums up the required values and writes them in the additional product field. After the value of the additional field through the settings for passing custom fields in action, transfer to quantity. I can also offer a revision directly to the action of exporting goods to opencart, so that they add up the availability of suppliers and warehouses and transfer them to quantity, it will take 2 hours.