Beginning 1 January 2021, companies issuing invoices under Portuguese law must proactively inform the Portuguese tax authorities about the number series expected to be applied on invoices, prior to being applied.
Once the series has been communicated, the tax authority issues a validation code for each reported number series. The validation code is then used as a piece of the unique identification number for invoices (ATCUD). The ATCUD comprises the validation code of the series and a sequential number within the series in the following format: “ATCUD:Validation Code-Sequential number”, and must be included in all invoices.
A QR code should also be included in all invoices. Technical specifications for how the QR code should be generated still remain to be published on the tax authority’s website.
More background and context for this new Portuguese piece of regulation is available here.