An invoice’s total is its subtotal plus its tax

AP and AR invoices: a total that does not equal subtotal + tax is refused with the sum, a total left blank is worked out, and an invoice with lines takes all three from its lines.

The total of a supplier or customer invoice is what the ledger posts, what the aging ages and what is paid, so it can never disagree with its own figures.

• Without lines: the total is the subtotal plus the tax. Leave Total empty, or change the subtotal or the tax, and the total is worked out. Type a total that is not the sum and the save is refused, saying what the sum is — "20.00 + 1.50 = 21.50, and 999.00 was entered".
• With lines: the subtotal, tax and total are the lines added up and cannot be typed. Change a line and they follow.
• An invoice saved with a mismatched total before this check keeps it until it is edited: open it, correct the total (or clear it) and save.