If you client gave you their credit card information you are able to pay on your clients behalf. You will first click "+Add New Payment" to the right of the proposal/ invoice. Then there is an option to "pay on behalf of your client" and enter the cc information there. You now have a made a payment for your client! 

**Important to note that you, the designer will assume the transaction fee when using this feature. If you would like to charge your client the transaction fee you can send the invoice to yourself and pay it as if you were the client.