Opinion of Advocate General Collins delivered on 4 October 2024.#European Commission v Republic of Malta.#Failure of a Member State to fulfil obligations – Article 20 TFEU – Citizenship of the Union – Article 4(3) TEU – Principle of sincere cooperation – Principle of mutual trust between the Member States – Grant of the nationality of a Member State – Special relationship of solidarity and good faith – Operation of an investor citizenship scheme – Naturalisation in exchange for predetermined payments or investments – Transactional nature of the naturalisation scheme, which amounts to the ‘commercialisation’ of Union citizenship.#Case C-181/23.