As stated in the Guidelines for Grant Applicants, page 20, section 2.1.2, please refer to Annex IV to the Standard Grant Contract for specific rules regarding procurement procedures, particularly to sections 2.1, 2.2 and 2.3.
You can find this annex (inside Annex F: Standard Grant Contract, zipped file), alongside other documents on the programme website, particularly in the following link: http://www.blacksea-cbc.net/index.php/eng/Documents/Guidelines-for-applicants
You will also find in this link, Annex G: Eligibility of expenditure by budget lines. Please refer to the following sections: 3. Equipment and supplies and 5. Subcontracted services (external expertise and services) for the rules on nationality and origin.
Please also refer to the Practical Guide to contract procedures for EU external Actions (PRAG) for a comprehensive definition, specific rules and exceptions of the rules on nationality and origin. (Sections 2.3.1 and 2.3.2) You can find the PRAG in the following link: http://ec.europa.eu/europeaid/work/procedures/implementation/index_en.htm
The first meeting of the Joint Programming Committee – body responsible for the preparation of the Interreg NEXT (Neighbourhood External) Black Sea Basin Programme 2021-2027 – was held on the 29th of January 2020 in Brussels, Belgium. The eligible participating countries of the new Programme involves ten states from the Black Sea Basin: Armenia, Azerbaijan, Bulgaria, Georgia, Greece, Republic of Moldova, Romania, Russian Federation, Turkey and Ukraine.