Some Korean websites do not work when I access them from outside Korea, or give errors even within Korea?

Many Korean sites require Korean phone verification or a domestic card, and some block foreign IP addresses. The fixes are to get a Korean phone number and the PASS app for identity verification, use a Korean card for payments, and if you're accessing from abroad, a VPN with a Korea server often helps. Some government and banking sites still require a certificate (공동인증서 or 금융인증서), which you set up through your bank.