We originally announced PAYDAY Credits would be coming to the game, and would only be exchanged for cosmetic items.
As part of Operation Medic Bag, we have instead moved various items that would be purchasable for PAYDAY Credits into the in-game store, and can be purchased for C-Stacks. One of these masks will be "Mask of the Week" and can be purchased for a great discount!
We have not yet announced any further plans with PAYDAY Credits.