I had the same issue yesterday. It turned out I already purchased too many items that I didn't have any credit left. Even though the credit count was on 800. After a refresh/restart the game updated my credit count and it adjusted it too 100.
Does this maybe help?
I'm getting this same issue - on top of my money being seemingly glitched, I'm not sure if I stopped earning money after a certain rank but it's been 100 for a few ranks despite saying that I've received another 100, I've restarted and everything but I'm just not earning money, it's been two ranks.
This is on top of losing 400 earlier that I was going to use for a torso piece.