You basically have to apply from the country in which you are based. There are about a dozen countries available, but I don't know how many offer invitations. UK and Brazil still offered invitations a couple of weeks ago.
If you have a US account, you need to do the surveys from a US IP address AND need to have a US telephone number to redeem your $s. IP based telephones do not work, in my experience.
Also to note, there are much more surveys available to US accounts than to the rest of the world. But if you cannot redeem due to lack of a telephone number it is of no use to do a lot of surveys...