CFDI40110

El valor registrado en el campo Descuento no es menor o igual que el campo Subtotal.

In English Descuento (the discount) must not be more than SubTotal.

error: the document is invalid

What the rule checks

As the rule set's publisher wrote it. The rule runs on every element the context matches, and fails where the test is false; the validator reports the line of that element.

Context
/cfdi:Comprobante
Test
not(@Descuento) or mx:dec(@Descuento) le mx:dec(@SubTotal)

Checked with CFDI 4.0