CFDI error 401 from expired or wrong CSD: renew digital seal certificate on SAT portal, reload in PAC and ERP, then test stamp a minimal invoice.
CFDI error 401 during Mexican e-invoicing typically means the CSD (Certificado de Sello Digital) is expired or not loaded in your PAC or ERP.
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View all CFDI guides →Log in to SAT and verify the seal certificate expiration date for the RFC.
Replace .cer and .key files in your authorized PAC dashboard.
Issue a small real invoice to confirm error 401 is resolved.
Usually an expired or mismatched Certificado de Sello Digital (CSD) for the issuer RFC, or the PAC does not have the updated certificate loaded.
On the SAT website using e.firma under Certifica tu RFC before the current certificate expires.