Error in the update with the product stock

Hello,

In one of the products in my online shop I have clicked on the Sync button, to synchronise the information coming from Aliexpress for this product.

The problem is that when I update it, it detects it as being out of stock.

However, on the Aliexpress website I see that there are still 837 products in stock.

Have I followed some wrong step?

How should I have configured by default the theme of the synchronization of the products?

On the other hand I wanted to know, aren’t the products supposed to be synchronized automatically or do I always have to do it manually?

Thank you very much.