If you downloaded the RO2 from WP, you will can only register your account at WP. To access the Aeria's RO2 server you need to download it from Aeria's site not from WP. And one more think: some RO2 clients deny access to the game from some countries, to fix this you need to go to the Computer's Control Painel and then open the Language and Region's window then change your country and language to a supported country and language. For exemple: if you're philippine and your country isn't supported, but US is then change your region to US and your language to english. If you doesn't know how to do this, here goes how to do:
do the following Start Menu>Control Painel>Language and Region, in the tab Formats change your country from your language to English (US) and in the tab Local change your country to US, then apply the new configurations. If you still cannot register in WP then try download the Aeria's RO2 Client.