CRP20115
El valor del campo Cantidad debe ser "1".
In English The Concepto of a payment receipt has Cantidad 1.
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[@TipoDeComprobante = 'P']/cfdi:Conceptos/cfdi:Concepto
Test
mx:dec(@Cantidad) = 1
Checked with CFDI 4.0