Once you get a message from a client they will have already added a credit card and agreed to your hourly rate. To log time you spend on work for them, send the slash command /log [minutes] into the chat. This will add the dollar value for the time to the clients "tab".
To charge a clients card, use the slash command /charge. This will charge the client's card the amount on their tab, email them a receipt, and reset their tab to zero. The /charge command does nothing if the client's tab is below $5.00.
To refund a clients card for a charge, send a message to support with the chat id and the amount to refund.