Garageband - Unable to complete In-App Purchase I would like to buy more instruments, loops and so on in the new Garageband. The problem is that if I choose 


  Garageband &rarr; Purchase more sounds


click Continue when it told me what I'm going to buy. I enter my Apple ID then click Buy when the App Store ask me if want to buy this In App Purchase. 

Then App Store tells me to renter my Apple ID password because it will ask me a security question. If I then enter my Apple ID I get redirected to an empty page (in Mac App Store)

I tried with reloading this page. I've restarted the Mac, logged out logged in in Mac App Store, I've read this article http://support.apple.com/kb/TS5275 (What accept button?). I have no more idea what to do.

Edit

Okay. I started looking closer and found some intressting logs. storeagent is logging normal things (requests) but then it suddenly logs 

Dock[201]: LaunchPad: __53-[LPAppManager(StoreSupport) _acceptStoreConnection:]_block_invoke app store xpc message error: Connection invalid


What does connection invalid mean? I don't know. I tried with using another internet access. No luck.
You won't be able to purchase IAPs for GarageBand unless the Mac App Store is logged in to the same account that 'accepted' the iLife apps.

Make sure you're logged in to the desired account, then open App Store &rarr; Purchases. If the iLife apps show as unaccepted, click Accept.