It appears to be a PIN for using Qantas points at BP. Open the Qantas app, click on the small card icon at top right, then the small "i" circle. Then select "In Store". It says that the "Reward Code" is what you need to use Qantas points at BP.
If that's what it is, this is really unimpressive -- calling this a "Reward" when it's anything but.