you get that for every lvl after 51…it’s repeatable
By the looks of it, you already got that reward once. There’s no more challenges left so the only way to get it again is by buying additional levels.
Overall that reward is there for those who bought levels or a deluxe version of the pass and did all the challenges too, so they don’t leave empty-handed.
What Armagodura said. You’ll have to spend crosscrowns to get the reward again, and if you keep spending crosscrowns, you can get it multiple times. They make it sound like you can earn it multiple times, but that apparently is incorrect.
You have to buy the battle pass to receive the gold. The infinity symbol hides the lock symbol. The other items show the lock symbol so you will not receive gold.