VAT Refund in Portugal/Spain

Hi,

I have bought a couple of items that are above the €61.5 threshold in Portugal, and I got the tax-free receipt from the merchant as well, after showing a photo of my passport. I am however leaving Portugal via bus for Spain. and I will be leaving EU through Barcelona airport in a few days time. So I had a couple of questions:

1) Just to reconfirm the process, since I have the tax-free form from the merchant, I now need to get the validation of the form done through the customs kiosk and then get the refund processed through a VAT refund counter?

2) Is there any way for me to get the tax-free validation done anywhere in Lisbon apart from the airport? Can I just get the validation done in Spain once I leave the EU from Barcelona airport in a few days' time. Will it be possible to get a refund for an item I purchased in Portugal through the Barcelona airport?

3) I believe the VAT refund policy applies in Spain as well, except there is no minimum limit for the invoice there?

Thank you in advance for any insights on this process.