The low account balance notification appears when you have less than $5.00 in your account balance. You can continue using service like normal as long as your account is positive $1.00, but once it goes into the negative your Master Switch will be turned off until it is at least $1.00 positive again.
How to Fund your Account Balance:
Step 1. Go to the Billing page.
Step 2. Under the My Funds section, select the first option from the dropdown menu “Fund my account a custom amount” and add whatever amount you wish.