Billing question

Out of know where it's saying there is a problem with my payment, I play one game and spend money on it and it only. And I haven't purhased anything in a while. The game developer will deny access if a payment was demeed unacceptable. I'm still playing no issues. This stupid reminder blocks me from downloading anything. I have looked everywhere to see a description of what they are talking about and I find nothing . I'm not about to just whip out my credit card anytime Apple says so. I need to see what iI'm being billed for