Case C-784/19: Judgment of the Court (Grand Chamber) of 3 June 2021 (request for a preliminary ruling from the Administrativen sad — Varna — Bulgaria) — ‘TEAM POWER EUROPE’ EOOD v Direktor na Teritorialna direktsia na Natsionalna agentsia za prihodite — 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)