Lasse, sorry your post wasn't answered so far. But hopefully, you are still evaluating and we can help here. Under the Browser App -> Configuration, you should see an Advanced Section on the bottom half of the screen. Expand a sub-section (which is usually collapsed by default) named "Customize your deployment". Once you expand that, you will see the AppKey that you need to use in the Javasript agent that you are intrumenting the page(s) with...
If you are still not able to locate this option, pls take a screenshot of what you are viewing under the Browser App -> Configuration screen and we will be happy to walk you thru that...