We look into all issues related to potential bugs. That being said, credit card verification is handled by a third-party provider, Stripe, which is an industry standard. They ensure user payment information is always safe and never exposed directly to us (we don't ever see user card numbers or process payments directly). Unfortunately because of this, we are only able to say that any credit card related issues are either connected with the form of payment or something, something on your bank's end, or something on Stripe's end.
We recommend to try a different credit card number, or to contact your payment processor to see if there are any holds or declined transactions on the account in question.
Alternatively, we also accept account balance refills via PayPal as another form of payment.
Feel free to Contact Us if you need additional support.