There could be a few reasons:
- The challenge period has ended by the time you completed it.
- You have not accepted the challenge (by tapping on Accept challenge in the challenge details page).
- For challenges which include placing orders online at FairPrice, the task will only be marked completed when the order has been delivered. If your order is still pending for delivery, the task and challenge will not be completed yet.
Please check the challenge details page along with the terms and conditions for more clarification.