How I buy mine:
1) https://www.warpportal.com/
2) Click "Power-Up" highlighted in blue at the top of the page.
3) Enter login credentials.
4) I'm greeted with the purchase page, asking to select amount of WPE I wish to buy and payment method.
5) Assuming you already have WPE, in the left side of the screen there should be a panel named "Game Accounts" with a list of game accounts associated to your WarpPortal account. To the side of each game account it displays how many points you have in them (in Ragnarok's case, that'd be Kafra Points) and also a "+" icon. Click the icon.
6) You're now in a page that allows conversion of WPE to Kafra Points. You'll notice it is divided in 4 tabs (at the top): Convert to Kafra Points, VIP Package, Ragnarok "Game" Coupons and Value Added Service.
7) Click on the second tab: VIP Package.
8) Select VIP plan and place order.
9) Confirm the purchase in the next screen. You're done.
That's how it works for ME, at least.