Can I get my refund at the Barcelona airport customs first ?

"First stamp, need to check the purchased items, how can you check when you have already checked in?"

First board the plane, pick up the ticket, label the luggage, and then take the luggage down to customs. It feels like this is right.

First check in, get the ticket, put luggage tags on, and then take the luggage down to customs. Otherwise the luggage doesn't know which country to go to.

First take the suitcase to the customs for inspection. They will open the suitcase for random checks. Then you can pack your luggage, get your boarding pass and check in. After that, go through security. Inside, there are two tax refund companies, one is Blue Tax and the other is Tax Free. If they insist on giving you Chinese yuan instead of euros, just pretend not to understand and only ask for euros. If they can't handle it, they will give you euros. Pretending not to understand has its benefits. I have used it several times in Spain. Hehe.