ANSWER:

Firstly, You should check your personal informations of your account. Have you filled in all of the blank of personal information category yet?

Secondly, You need to choose the options which are offered by the system in the State and Province

Thirdly, You have to fill in correctly your Post code where you live in

ex: You are living in Ho Chi Minh city is 70000

Noted: 084 and +84 are not the zip post code of Viet Nam.

Here are the form