When you install the application from AppExchange, you are installing a trial version. To continue using the app, you will have to make payment by providing your credit card information. See below for how to purchase.
Step 1: Login to AppExchange
1. Go to AppExchange and Login
2. After login, go to My Installs & Subscriptions
3. Look for the app that you would like to purchase and click Buy Now.
4. You will then be redirected to the app and prompted for payment information