Judgment of the General Court (Fourth Chamber) of 14 December 2022.#Green Power Technologies, SL v European Commission.#Arbitration clause – Seventh Framework Programme for research, technological development and demonstration activities (2007-2013) – Grant agreement – Eligible costs – OLAF report finding certain expenses incurred to be ineligible – Repayment of sums paid – Burden of proof – Regulation (EU, Euratom) No 883/2013 – Obligation to state reasons – Unjust enrichment – Action for annulment – OLAF report – Act not open to challenge