Mark a client tax-exempt

Open the client's record and turn on tax exemption. You can record the exemption type, a certificate number and expiration, notes, and upload the certificate file (stored privately).

Once flagged, new proposals and invoices for that client zero out sales tax and show a “Tax exempt” line, and the editor shows a banner so you know why tax is $0. The exemption is enforced on the server, not just in the UI.