Try in the late night hours. I didn't use a VPN. I tried for 5 days and was going to buy with another airline but every airline in Peru had bad reviews about the ticketing so I went back to LATAM. When I finally got it to go thru with a MC, the cc company declined it for my approval and then said try again but when I tried again no luck. That was late at night so I decided to wait until late at night the next night. The MC said try a different card this time, so I went with the AMEX and it worked. I used the AU site both times.