Compiled as of bc5ff34

The DefaultPrize in the main config is rewarding on parkour course completion in addition to economy payout defined. Would it be possible to only reward in-game currency for the course?

  Prize:
    Enabled: true
  DefaultPrize:
    Material: DIAMOND
    Amount: 1
    XP: 0

Price:
  Kit: 0
  spawn:
    Finish: 25

Setting the following only disables the economy payout, not the diamond reward.

  Prize:
    Enabled: false

This has been mentioned before - to disable the default prize just set "Amount: 0" in the config.
I'm pretty sure setting
Prize:
Enabled: false
disables both the default and custom prizes.

Setting prize false does not. I was still rewarded a diamond. It just disabled the economy payout.

As @steve4744 mentioned, setting prize to true allows the player to receive any prize once completed, so this needs to be true. Setting the amount to 0 will give the player no physical item for completion.

Assuming you've resolved this now; reopen if not.