Purchase at Runes of Magic using a Rixty account:
Download Runes of Magic from http://www.runesofmagic.com.
Start the game and choose "Recharge Diamonds" on the opening screen.
Enter the email and password of your Runes of Magic game account.
Press the "Buy Diamonds" button.
Choose the amount of Diamonds you want to buy, then select Rixty as the form of payment. Press the "shopping cart" button at bottom to continue.
Login to your Rixty account and complete the purchase. If you need to add funds, click a payment method and follow the prompts.