Thank you for playing Disney Twisted-Wonderland.
For the ongoing Sam's New Year Sale 2025 event,
Regarding your concern about being notified of a mission completion despite having no way to claim rewards for said mission, it is because the condition of the "Sam's New Year@Sale 2025 (2)" mission have been cleared first before the date wherein the rewards will be available to claim, which is from January 9th.
However, please rest assured that you will be able to claim the rewards from January 9th.
We apologize for the inconvenience and thank you for your understanding.