That's a (Plarium's) payment provider issue.

I can get such, for example, if I buy too many too fast - cc company stops approving payments due to fraud alert. Solution was to make sure your cc has alerts / notifications active and sent to your phone / e-mail. Watch for such when buying, and be ready to react reasonably promptly. [Missed a sale or 2 because of this - by minutes.] Once you know what's going on, you're ready - when it happens again, approve the notification, try again, and get on with your day. 

Two things you can do:

1. Start a ticket with Plarium to find out what's what. Be ready with the date and time of when you tried. They can look things up. They don't have all the details, the payment provider does but they don't, but they may have enough to help you figure out next steps. (Payment providers are usually a good thing - if Plarium doesn't have your cc details, if hacked there is nothing they have to be leaked.] KaW Support - Create Ticket 

2. Call your cc company. Ask about an attempted purcharse from Plarium around that date and time - they should be able to see that a purchase attempt was made, and why it was denied. e.g. You may have international purchase restrictions set on your account. You can then react as you feel best - permit such purchases, only from certain areas, whitelist Plarium, or whatever other permission switch you need to have them set on your account - for next time.

Good luck - it's irritating when this happens, but usually makes sense after the fact. Often better safe than sorry, I suppose.