If you are trying to upgrade, but getting the message 'Problem while processing your payment method. Please verify your payment method details', first please check that your payment details are correct.

If you're sure that your payment details are correct, then most likely your bank or credit card company is blocking the transaction. 

Sometimes banks or credit card companies block the transaction because we are a Hong Kong based company.

You should be able to unblock the transaction by giving them a quick call.