Starting August 5 2013, IMVU will require you to verify your email address with them BEFORE you can receive any credits from any reseller.
Checking if you've already verified is simple, just view IMVU's verification page. If you have not verified your email address with them, you'll need to click their link to have the email re-sent to you. Then click the link from within that email. Make sure you're logged into the correct avatar that you need to verify the email address for.