For DLC bonus content problems click here.
On PS4 you can play the game on any Playstation 4 console even if it's not from your region, but in order to activate DLC it has to be from the same region as your PSN account. This is due to the Playstation Store being region locked, not the console itself. Therefore if you are unable to redeem your DLC code, you should check the region on the disc and the region on the account on which you are trying to redeem the code, if they do not match then your issue is due to PlayStation Network regional limitations.
The disc version of Rocket League (Collector's Edition) is either from the region US/JP or EU/AU. To determine which one you have, you can check the CUSA code on the disc:
US / JP = CUSA-01163
EU / AU = CUSA-01433
For disc problems click here. If you need assistance replacing your physical copy, the right place to get support is from our partners over at Warner Brothers games. You can contact them at: support.wbgames.com/hc/en-us