How do I configure a callback URL?

You can set up your callback URL via the Old Customer Portal.

Under the "Account" tab on the Customer Portal Dashboard, click on:
API Account Details > HTTP CALLBACK URL
(This will be deprecated starting December 20, 2017 onwards.)

If you are using the New Customer Portal (https://app.wavecell.com).
Do request for our support team to setup a CALLBACK URL for you.