1. In your WordPress admin under the Media menu, select DropBox Audio.
2. On the DropBox Audio page, click on a button at the top right
side called "your license info" (here is a screenshot of that button):
This will open up your license info at the bottom of the page:
There you should be fine to enter your details.
If you follow these steps and are still unable to get to your
license info, please send me a WordPress admin login so
I can login to your admin and see what is going on. Please
include username, password and admin link. (you can use
an existing username and password, or create a temporary one)
I hope that helps.