OS X Beta Upgrade Says Redemption Code Already Used
Issue occurs when you sign up for the OS X developer program and try to install OS X developer copy of El Capitan for example on more than one Mac.
If you are experiencing this error, try holding down the ALT/Option while clicking on Purchases. You should see a list of recently downloaded items (which will include OS X 10.11) if that was already downloaded on another Mac.
Specific to El Capitan: You cannot install Beta 3 from scratch, you’ll be downloading Beta 1 and updating to Beta 4 (or whatever the latest is from your latest OS X version downloadable from the list in Purchases.
