Opinion of Advocate General Campos Sánchez-Bordona delivered on 10 December 2020.#„TEAM POWER EUROPE“ EOOD v Direktor na Teritorialna direktsia na Natsionalna agentsia za prihodite - Varna.#Request for a preliminary ruling from the Administrativen sad - Varna.#Reference for a preliminary ruling – Migrant workers – Social security – Legislation applicable – Regulation (EC) No 883/2004 – Article 12(1) – Posting of workers – Temporary agency workers – Regulation (EC) No 987/2009 – Article 14(2) – A1 certificate – Determination of the Member State in which the employer normally carries out its activities – Concept of ‘substantial activities, other than purely internal management activities’ – No assignment of temporary agency workers in the territory of the Member State in which the employer is established.#Case C-784/19.