24-Hour PIN: How to File Your Tax Returns Without a Digital Certificate

One of the classic barriers to dealing with the tax authorities online has been the digital certificate: installing it, renewing it, moving it from one computer to another. As an alternative, the Spanish Tax Agency (AEAT) has for years offered simpler ways to identify yourself, among them the so-called 24-Hour PIN, part of the Cl@ve system. It’s worth understanding what it lets you do, what it doesn’t, and how it fits into the day-to-day operations of a freelancer or small business in 2026.

What the 24-Hour PIN is and how it works

It is a temporary identification method: you register in advance in Cl@ve and, each time you need to access a procedure, you request a code that is sent to your mobile phone and expires after a short time. That code, combined with your national ID (DNI) or foreigner ID (NIE) and other verification details, proves who you are without having to install any certificate on your computer.

Registration can be done online or in person, and requires proving your identity with sufficient safeguards. It is a one-time step, but one you shouldn’t leave until the last day of a filing deadline. In addition, the AEAT has been adapting its identification methods, and the Cl@ve mobile app has gained prominence over the SMS code, so the prudent approach is to check the electronic office to see which options are currently active.

What you can do, and where the limits are

With Cl@ve you can carry out many common procedures for individuals: checking your tax data, downloading certificates, accessing notifications or managing your income tax return. For a freelancer filing their own taxes, it may be enough for certain forms, as long as the specific procedure accepts this method of identification.

That said, a PIN doesn’t work for everything. Some procedures still require an electronic certificate or an equivalent accreditation, and this is especially relevant for companies: legal entities usually need the company’s certificate or a valid power of representation. Nor is it the most convenient method when you file forms regularly or in batches, or when you act on behalf of third parties, where a representative’s certificate or a registered power of representation is the norm.

Another practical limit is security: a code sent to your phone depends on that phone. If you change your number, lose your device or someone gains access to your line, access to your tax data is compromised. Treat that data with the same care as your online banking.

What this means for your business

If you are a freelancer and don’t yet have any identification method set up, registering in Cl@ve is a low-cost step that keeps you from being locked out when a notification arrives or you need to download a receipt. Do it well in advance, not once a filing deadline is already running.

If you file your own quarterly returns, check before each deadline that the method you use works for that specific form. It is better to discover an incompatibility days ahead than on the last day, when a late filing can bring surcharges.

If you manage a company, don’t count on the PIN as a substitute for the company’s certificate. Check its validity, who holds it, and whether there is a power of representation in favor of your accounting firm, so that filings don’t depend on a single person.

And if you’re unsure what suits you best, think about frequency: the more filings and the more people involved, the more sense it makes to have a stable system based on a certificate or power of representation, keeping the PIN as a complementary route for queries and one-off procedures.

At Zythos Business we help freelancers and small businesses sort out this part that almost nobody sees: which identification method to use in each case, powers of representation before the AEAT, certificate management and deadline calendars, so that filings are made on time and with the right safeguards. If you’d like to review how your access to the tax authorities is set up, we’ll be glad to give you a hand.