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.