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george

Hi everyone,

I’m dealing with a strange issue that started right after upgrading one of my databases from Odoo 17 Enterprise to Odoo 18 Enterprise. The problem appears on invoices that come from Subscriptions. (I dont have a normal sales on this project, they sell only services with subscription)


What’s happening

When I try to create a credit note using the standard “Add Credit Note” button on a posted customer invoice, Odoo throws this error instead of generating the credit note:

The unit of measure Units defined on the order line doesn't belong to the same category as
the unit of measure False defined on the product. Please correct the UoM on the order line
or on the product. They should belong to the same category.

The key part is that Odoo says the product’s UoM is False, even though in the product form the UoM is definitely set and it was working fine before the upgrade.



What I already checked

  • The product UoM is correctly set (in the UI and in DB).

  • The sale order line UoM is set.

  • Invoice line UoM appears normal.

  • All UoMs belong to the same category.

  • No custom modules involved.

  • I verified the DB entries directly (product_template, sale_order_line, account_move_line).

If anyone has run into this before, or knows how to properly fix UoM data for subscription invoices in Odoo 18, I’d really appreciate any guidance. Thanks in advance!


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Cybrosys Techno Solutions Pvt.Ltd
Best Answer

Hi,


The issue is caused by subscription-generated invoices that, after the upgrade from Odoo 17 to 18, contain hidden NULL values in the product_uom_id field. Even though the UI shows a correct unit of measure, the database value is missing. When you try to create a credit note, Odoo re-checks the UoM compatibility, sees that one side is False/NULL, and raises the “UoM category mismatch” error. This only affects subscription invoices because Odoo 18 changed how recurring invoices are generated, and some migrated records lost their UoM links.

To confirm the issue, you can inspect the invoice lines directly in the database, where you will likely find missing UoM entries. Fixing it requires updating those invoice lines to restore the correct UoM based on the product, and also correcting the subscription templates so that future invoices include proper UoM values. For a long-term solution, a small custom module can enforce that Odoo always assigns a UoM whenever it generates invoice lines.

In short, this is a data integrity issue caused by the 17→18 upgrade, and the solution is to repair the affected invoice lines and prevent the problem from recurring by ensuring subscription products always carry their UoM through to invoice creation.


Hope it helps

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