Select MediaTailor Ad Configuration from the left hand tabs:
If the navigation bar is hidden, click to open it.
Give the configuration a memorable name of your choice.
Paste your Channel Assembly channel URL in to the Content Source field. Remember your URL can be found under the Channel Assembly, Channel Output tab. DO NOT include the manifest name.
Your content source should end with a forward slash.
Copy the following string into the Ad decision server field
Your configuration should look similar to this:
Leave all other setting blank or at defaults.
Click Create configuration at the bottom of the page