When you sign up for Podcorn or any other services, you will get a prefix you will need to add to your BlogTalkRadio feed.

Once you have the prefix, you will want to log into your BlogTalkRadio account, and visit the show tab on the left. From here, you can scroll to the bottom of the page, and enter the prefix in the designated area as seen in the screenshot.

Please note, to be able to add a prefix, you must be a premium account.