At signup, your payment method was billed and that amount applied as a credit towards your account for Usage and Subscription charges. When your balance reaches the "Balance Threshold", your Payment Method will automatically be charged the "Replenishment Payment Amount".
By default your account terms include:
$25 Credit Limit for new customers
$1.00 Balance Threshold
$25.00 Replenishment Payment Amount
The Balance Threshold and Replenishment Payment Amount can be viewed and managed on the Payment screen under the Billing menu.
Note: As your monthly usage increases, it is recommended to increase the Replenishment Payment Amount to avoid any interruption in services. If your balance reaches your credit limit, your services will be suspended until a payment is made to your account. Automatic Payments are only performed 1-time per hour. 1-time Payments can be performed at any time.