Can't download basic lessons in GarageBand
I've just bought a keyboard, connected it to my Mac and started GarageBand. The "Intro to Piano" lesson works great, but I can't access any of the other lessons. I go to "Lesson Store" and click the download icon at the bottom right:
This brings up the dialog asking you to purchase (but doesn't give a price?):
Click "Continue". It asks for me to log in to my AppleID. This brings up the next dialog which says that I've already purchased this.
Afterwards, it asks me to log in to my AppleID again, but leaves me at the same "Add more lessons to GarageBand" dialog.
If I go to the App Store, there's an old version of GarageBand (6.0.5), but nothing otherwise that I can see.
If I go back to the Lesson Store again, I can get to the same purchase dialog, but it won't ask for my AppleID. Clicking the continue button does nothing.
So what gives? Have I already purchased this, or do I need to purchase it again?
MacBook Pro with Retina display, OS X Mavericks (10.9.5)