Hi,

By default, Odoo does not fully support this process. While you can manually create a credit note without referencing an existing invoice, Odoo does not allow linking a lot or serial number directly to invoice lines. Also, the system cannot automatically fetch the product cost based on the lot, as lot traceability is handled at the stock movement level rather than the accounting level.

To address this, the recommended approach is to extend the account.move.line model by adding a field for selecting the lot or serial number and configuring logic to auto-populate the cost price based on that lot. When the credit note is validated, the system can automatically generate a corresponding return picking, ensuring both accounting and stock are synchronized. This allows accurate cost and lot tracking for the returned goods.

If customization is not an option, the workaround is to manually create credit notes and separately record the lot numbers in notes or text fields. The manufacturer can then manually adjust the pricing and process a stock return through the inventory module. Alternatively, there are third-party Odoo apps available that enable lot or serial number selection in credit notes and automate product cost fetching, offering a more streamlined solution for managing such returns.

Hope it helps