Who actually qualifies
The Autoridade Tributária e Aduaneira, Portugal's tax and customs authority, defines an eligible traveller as a private person with no domicile or habitual residence in the European Union who buys goods in Portugal for private use and carries them out of the EU in personal luggage within three months of the purchase. Personal luggage means carry-on or checked bags that belong to and travel with you, so goods shipped separately do not qualify.
The purchase also has to look like personal shopping rather than a business order. The tax authority evaluates this case by case, weighing the nature and quantity of what you bought.
What the retailer has to hand you
This part happens in the shop, not at the airport. The retailer must issue a full invoice, not a simplified receipt, and it needs to carry your full name, date of birth, identification document details, your country of residence, a Portuguese tax number if you have one, and a reference to the legal basis for the exemption, Article 14(1)(b) of the Portuguese VAT Code (CIVA). The invoice is issued in duplicate: you keep the original, the retailer keeps a copy.
The net value of the invoice, VAT excluded, has to reach 50 euros. That is a lower bar than several neighbouring countries, so combining smaller purchases with a single participating retailer on the same visit can be worth doing before you check out.
Some retailers ask for a deposit equal to the VAT amount, either in cash or as a card authorisation, and refund it once your export is confirmed. Whether a shop works this way or not is a decision the retailer makes, not something the tax authority mandates, so ask before you pay if it matters to how you pay in Portugal.
How the kiosk actually decides
At departure, you go to an e-Taxfree kiosk in the customs area rather than a manned desk. The system reads the identification document you used to buy the goods and your boarding pass, then checks the invoice electronically against the eligibility conditions.
A green light means the exemption is certified and you are done. A red light means the system needs a human to look at it, and you then have 24 hours to present yourself, your goods and your documents at a customs office to get the invoice certified manually. Miss that window and the exemption on the flagged items is lost, not just delayed.
Bring the same identification document you used in the shop, your boarding pass, and the goods themselves in unused condition and original packaging. The kiosk can grant total or partial certification, so if you bought from several retailers on one trip, one invoice can fail validation while another passes.
If your itinerary connects through another EU country before your final non-EU destination, present both boarding passes at the Portuguese kiosk so it can confirm your actual exit point is outside the EU. If you instead clear final EU exit somewhere else, that other country's customs procedure governs the validation, not Portugal's, and the fact you bought the goods in Lisbon does not change that.
There is one more route: if a retailer's paperwork ends up needing to be validated abroad rather than in Portugal, the signed and stamped documents have to reach the Portuguese seller within 150 days of the sale, or the exemption is denied retroactively.
Where the money actually shows up
This is not a refund in the sense of a payment coming back to you from the state. The exemption works as non-taxation at source: once the retailer's system confirms your export has been validated, VAT was never charged, or the deposit you left is returned. Where a financial intermediary is involved, Portuguese rules require that reimbursement within 15 days of the tax authority's certification.
If you are shopping for cork or canned fish or other typically Portuguese goods as gifts, keep the invoices with the rest of your travel documents rather than in checked luggage, since you may need to produce both the goods and the paperwork together at the kiosk.
What commonly goes wrong
Two failure points show up more than others. The first is arriving at the kiosk with goods already checked into the hold: since you may be asked to present the items themselves, packing them where you cannot reach them before security defeats the process. The second is timing: if the kiosk returns a red light late in your layover, the 24-hour window to reach a customs office can be tighter than it looks once you account for a connecting flight.
A smaller but recurring issue is retailers who are not actually part of the electronic system. The invoice itself needs to be built for e-Taxfree from the start; a shop that is not registered cannot retroactively issue one after the fact.
What to check before you rely on this
Thresholds and specific retailer procedures can change, and the tax authority's own FAQ page is the place to check the current rule rather than a summary. If you land at Humberto Delgado Airport with a tight connection, build in time for the kiosk step before security rather than treating it as something you can skip if you are running late.