Why does the VAT rate show zero, and why won't the system save?

Our system currently cannot send ZATCA a line without VAT (0%), because an exempt line needs an exemption reason the system doesn't support yet. So it refuses to save when the rate is zero.

• Check that the VAT rate is 15% in Settings → Tax & E-Invoicing; new invoices take their rate from there.
• On an engineering project invoice, the rate comes from the project's contract when it has one; check the VAT rate on the contract lines.
• At the POS, check the VAT rate on the product card.