We want to have an option to block the entry of a free adjustment when adding a product to an invoice.

This is to ensure that users only use predefined products to invoice/reimburse, so that accounting information is coherent.

Indeed, by nature a free adjustment is not linked to a product and therefore not linked to a specific accounting category.

What is the problematic use case?
When we invoice/reimburse a product, our teams need to invoice an existing product so that the correct accounting category passes through our accounting interface (api).
But users make the mistake of refunding a free amount directly from the free field (left-hand side of the screen) instead of refunding a product (by selecting it on the right-hand side). In this way, we generate accounting entries via the api that are not linked to specific accounting categories (because the free field does not correspond to a specific product and therefore to a specific accounting category).

It is not acceptable to have amounts in the accounting that are not linked to specific accounting categories.

Thank you for your understanding.