So my friend bought 5.5k RC, it's already in the game. but every time he tries to buy something with it, it says the purchase "Failed". First we thought he needs to be level 3, tried, didn't work still. Then we thought he needs to be level 5, still doesn't work. What the hell is he supposed to do now after spending 50 dollars for this damn game.
A Visa/Mastercard/AMEX Gift Card should work without any issues. You may be required to specify a postal/zip code on the card though as it may be declined without one. In most cases you'll be linking the gift card to your PayPal account.