There might 4 possible reasons for this:
1. Your Task is listed on the Offerwall’s ‘In Progress’ tab:
Tasks are removed from the “In Progress” tab 60 days after you have clicked on them, and you will not be able to open a  Customer Support ticket after that period.

2. Less than 6 hours have passed since you clicked on the Task:
Tickets to Customer Support can only be opened 6 hours after the first click on the Task, and until 60 days after the click (unless otherwise specified).

3. The offer is marked as completed or blocked

4. You are receiving an error message when trying to click the "missing rewards" link:
This means our system has blocked the option to open a ticket due to the use of VPN or because you have already been rewarded for a Task by the same title.