Simply stated, credits equal money. Every month you get 1000 credits with your subscription. So, what can 1000 credits buy?
That depends on a couple of things.
For example, if you have 100 contacts, you can send an SMS text out to the list 10 times a month or an MMS text 5 times a month.
If your credit balance hits 100, you will see a message at the top of the page. The message is a link to where you can purchase more credits. Any credits you purchase will stay in your account until used, rolling forward every month.
If your credit balance hits 0, you will be redirected to the page where you can buy more credits.
No, you do not have to purchase credits, but you will not be able to use many of the features of KingdomText until your next subscription payment. 1000 credits will be added when the payment is made.
Remember that both the monthly and any purchased credits roll forward every month.