Steam have updated their checkout process in an attempt to prevent people from using VPN's etc to get cheaper games.
When you make a purchase you are required to use a cc from the country you are claiming to be from.
(Gift cards cant be used for first purchase when you first change country location)
So lets say, you are making you first purchase in "Brazil" to buy a game
you are required to use a Brazil Based Credit Card to confirm you are a resident of that country.
Once you have done this you can then use Gift Cards etc
Each time you country changes (due to VPN or from actually moving to that country) you need to use a locally issued cc to establish your residency.
if you do not have a local cc you can contact steam support who will ask for documents to establish your residency then they will unlock your account to use the store in that country.
Also should note, first purchase since the change. So even if you have bought from a different country you will be required to do this next time you make a purchase.
more info:
https://www.pcgamer.com/au/steam-has-been-making-it-tougher-…
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