The only reason you wouldn’t get paid for a task is if you didn’t complete it.
The 2 main reasons why this happens are being screened out of a task or the task having already expired. You can read more about screen-outs here.
Make sure to double-check your completions tab in the app as this will show you the status of your task.
If you still think you have completed a task but you didn’t get rewarded please make sure to contact our support team with details of the task, so we can investigate this further.