Case C-538/19: Judgment of the Court (Fourth Chamber) of 6 October 2021 (request for a preliminary ruling from the Curtea de Apel Constanţa — Romania) — TS, UT, VU v Casa Naţională de Asigurări de Sănătate, Casa de Asigurări de Sănătate Constanţa (Reference for a preliminary ruling — Social security — Sickness insurance — Regulation (EC) No 883/2004 — Article 20(1) and (2) — Medical treatment received in a Member State other than that in which the insured person resides — Prior authorisation — Conditions — Requirement for a report prescribing treatment, drawn up by a doctor of the national public sickness insurance scheme — Prescription, by way of a second medical opinion, drawn up in a Member State other than that in which the insured person resides, of an alternative treatment which has the advantage of not causing a disability — Full reimbursement of the medical expenses incurred in respect of that alternative treatment — Freedom to provide services — Article 56 TFEU)