Hello Ray, thank you very much for the link. I've recreated this configuration with the current odoo SaaS 18.1 but something is not working properly: I need to validate one delivery, then return everything, validate the scond delivery and finally the receipt.

Here are the operation types:

Here is the route and the rules:

The rule has been assigned to the product:

After I confirm the sales order, only one delivery will be created:

After validating the delivery, I can click on "Return" and then on "Return All":

At this point, two deliveries have been created:

After (manually) validating the second one, finally the receipt will be created:

After having validated the receipt INR00001, the stock report will show 1 t on the product available. At this point, the sales order has 3 stock movements:

What am I missing?

It is definetely not the negative price of the product in the sales order as it displays the same behavior:

Have you seen https://www.odoo.com/forum/help-1/route-operation-for-create-a-receipt-on-a-sales-order-185733 ?