To set up your Payment Method click on Account page at the top and from there click on Billing – Overview
In the Billing-Overview page click on the Setup Billing button and in appeared modal click on Next button. Once the Amount to add to your account now modal will display, select the amount from drop down menu you want to add to your account. Click on Next button and in appeared modal (Add Card) fill your details in. After that, click on Purchase button. Click on Done button in confirmation modal.
Once done, you can set auto-recharge by clicking on Enable Auto Recharge button. Select the amount from drop down menu you want to add to your account and click on Enable button Once this done, your account will be automatically charged the amount you have selected form drop down menu, when your call credit drops below 10$