Why am I blocked from selecting a tax on this item?

The system blocks you from applying any tax rate above 0% on a specific item when that item (or its associated client) matches one of the Tax Exemption Rules configured on the account. This block depends on the exemption rule’s settings as follows:

• If the rule is set to “Clients” only: the exemption blocks the tax if the client selected on the invoice matches the conditions (whether through direct selection, category, or nationality).
• If the rule is set to “Products” only: the exemption blocks the tax if the item itself (or its category) matches the conditions.
• If the rule is set to “Clients and Products” together: this depends on the configured Logical Operator; if it’s set to “Check Only One Condition“, a match on either the client or the product is enough to trigger the block. If it’s set to “Check Both Conditions Together“, both the client and the product must match.

To check the reason for the block in your case, review the “Tax Exemption Rules” settings from the Invoice Settings screen, and confirm the conditions configured for clients and products.