Originally Posted by Palal

So theoretically, if you have a single ticket, I've successfully gotten my VAT refund in LIS. If you don't manage to do it, you'll need to get your form stamped by customs in MAD and then send it in to Slovakia to be processed (and possibly never heard from again).

I would suggest putting your VAT items into checked luggage and going to the customs office BEFORE checking them in. Once you've done that, they'll validate things, and you can then check your bags. Once airside in LIS, you'll have to go to a machine to scan a QR code and the VAT refund will be processed automatically.

Again, this all presumes you're all on the same ticket and that you process VAT with customs in LIS BEFORE checking in bags.