After a document number series is configured in Sovos VAT Certified eInvoicing - Portugal, it cannot be modified. This creation process is only possible after communicating with AT (Autoridade Tributária e Adueneira) and receiving the validation code. That is because the validation code must be configured within Certified eInvoicing during the creation of the number series. After creating multiple number series with their respective validation codes in Certified eInvoicing, it is possible to issue fiscal documents whose ATCUD (Código Único de Documento da AT) and QR code will be generated automatically. For this to happen, each document issuance request must reference the name of the number series defined in Certified eInvoicing and the corresponding AT validation code.