The answer to this question is provided by the European Commission.

Articles 172-175 of Directive 2009/138/EC (Solvency II) provide for rules applicable to third-country reinsurers operating in the Union.

Those Articles lay down, together with the corresponding delegated acts, the conditions under which a third country regime for reinsurance is to be considered equivalent or not (including on a temporary basis). Reinsurers established in third countries that are subject to an equivalence decision have a right to provide services in all EU Member States. In the absence of an equivalence decision, EU Member States retain the right to determine the conditions under which third country reinsurers may provide services in their respective territories.

Article 211 of Commission Delegated Regulation (EU) 2015/35 sets out the conditions under which reinsurance contracts can be recognised as risk mitigation techniques. This regulation is directly applicable in all Member States and supersedes national legislation. Its provisions apply to contracts concluded by third country providers either under an equivalence decision or under national regimes.

Disclaimer provided by the European Commission:

The answers clarify provisions already contained in the applicable legislation. They do not extend in any way the rights and obligations deriving from such legislation nor do they introduce any additional requirements for the concerned operators and competent authorities. The answers are merely intended to assist natural or legal persons, including competent authorities and Union institutions and bodies, in clarifying the application or implementation of the relevant legal provisions. Only the Court of Justice of the European Union is competent to authoritatively interpret Union law. The views expressed in the internal Commission Decision cannot prejudge the position that the European Commission might take before the Union and national courts.