Article 13a 4.

Where an indirectly connected Member State provides a voluntary contribution on the basis of market-based measures to the requesting Member State pursuant to paragraphs 1 and 2 of this Article, fair compensation shall not exceed reasonable costs and may include the costs referred to in Article 13(8a), second subparagraph. The final amount of fair compensation shall be subject to the ex post control mechanism described in Article 13(8c).