I have all the required stuff. (I did that already).
I have checked your account and don't see the dress or the required base listed. Did you purchase using an account different from the one where Character Creator 3 is registered? If so that will be the problem. All content packs have to be registered to the same account as the software they are intended for.
If you did purchase the content using a different account, please contact Customer Support using the link below and they will be able to transfer the content into your main account for you.https://www.reallusion.com/CustomerSupport/UserEx/QForm.html