The exact rules and regs vary around the world. I usually recommend that people check out their national writing union if they have one.

There are cases where you can join a society in another country - eg if your country doesn't yet have a collecting society, but it's something you would need to check out with the society you wanted to join.

I wrote a more detailed post that might be worth checking out - I'll put the link below - also check the comments where there is further info and some further links to other societies.

Sorry, I don't have any detailed information for Portugal but as part of the EU I'm sure they have something in place. The article below has a link to the international umbrella organisation - which you can't join as an individual but which has info on its website about societies around the world.

https://writingcooperative.com/collecting-societies-exist-to-boost-your-income-c81f7a197f9f