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Local compliance context

What the Tax Authority requires from invoicing software (and how SimpleSum complies with the rules)

Choosing invoicing software is not just an operational decision: it is a compliance decision. The Portuguese Tax Authority defines clear rules for a program to be considered certified. In this article we summarize the main requirements and explain how SimpleSum was designed to meet them.

SimpleSum team2 min read

The Tax Authority (AT) defines a set of technical and functional requirements so that invoicing software can be used safely and compliantly. The objective is to guarantee the integrity of documents, the traceability of operations and the prevention of tax fraud.

AT's main requirements for invoicing software

Among the various technical points, The following stand out:

  • Sequential numbering by series – each series of documents must maintain a logical and uninterrupted;

  • ATCUD – all fiscally relevant documents must include the unique document code assigned by AT;

  • Digital signature – documents must be digitally signed to ensure integrity and impossibility of undetected changes;

  • QR Code – invoices must include the QR Code with the fields defined by AT;

  • SAF‑T export (PT) – the system must allow exporting the SAF‑T file in the official format;

  • Event logging and audit – sensitive operations must be recorded to ensure transparency.

  • Impossible to delete issued documents – corrections are made via credit notes, not by direct editing.

As SimpleSum was designed to comply with these requirements

SimpleSum incorporates these principles into the very core of the application:

  • Rigorous management of series and sequential numbering, avoiding holes and inconsistencies;

  • Generation of ATCUD before marking a document as issued;

  • Use of RSA digital signatures with keys stored in security;

  • Automatic generation of QR Code in accordance with AT specifications;

  • Export of SAF‑T prepared for submission and cross-referencing data;

  • Recording in AuditLog of critical actions performed by users.

Practical benefit for the user

In practice, this means that anyone using SimpleSum can focus on managing their business while the system ensures compliance with tax obligations. The application is designed to be simple on the surface, but deeply aligned with the AT underneath.

For freelancers and small businesses, this combination of usability and compliance reduces risk, simplifies inspections and gives confidence in the daily relationship with the Tax Authority.

Tags

#Billing compliance considerations
#Document controls
#Local tax authorities
#SimpleSum
What the Tax Authority requires to invoice | SimpleSum