Credits can be used in-game for the rewards system, which is currently used to unlock classes for use in Classic mode. Credits can also be obtained through normal gameplay at a more-than-reasonable rate. More rewards are going to be added in the near future.
We are working on an automated system to add purchased credits, however that system is not available yet.
Until then, we are manually processing orders. We are going to process orders in under 24 hours (and often much, much faster than that)
If you have any questions, here’s our contact info