Judgment of the General Court (Ninth Chamber) of 10 December 2025.#Silex Ipari Automatizálási Zrt. (Silex Zrt.) v European Commission.#Research and technological development – Horizon 2020 Framework Programme for Research and Innovation (2014-2020) – Recovery of sums unduly paid under a grant agreement – Challenge as to the validity of a contractual debt which has become final – Legal certainty – Inadmissible plea – Principle of good administration – Duty of diligence.#Case T-653/22.