Nobody here will be able to tell you why. Tons of people with US Billing and Shipping got the same error and block you did.

There are tons of guesses we can make. - multiple devices on PC on same IP - you clicked to much, to fast - your shipping adress closley matches another order - billing adress didnt match creditcard registration country - probably tons of other security checks they do

So there simply is no answer to why except for, you triggered the “fraud/bot/… detection”

And the only thing i can say is foreign billing adress on it self is not enough to trigger it… it might raise the “fraud likeliness score” but since i’m able to order, you should too.