When requesting a call with an expert, you'll be prompted to provide your credit card information. You'll be charged at that time for the initial call amount based on the rate and duration scheduled.
Following the call, charges will be adjusted based upon the expert's rate and actual length of the call. (not the approximate length you entered for the call request) minus any promotional codes entered. The member will be billed for any time that the call runs over beyond the original scheduled time or credited any balance if the call runs shorter than originally scheduled. To add a payment option, simply go to Account > Settings > Credit Card.