Russia in 2019 and 2020 took advantage of this four times, twice a year, and in this way its not exceeding allowed number. All four permits were for Russian military planes, which were intend to deliver weapons and special equipment to Serbia.
At the same time, it is clear that Russia has found a way to circumvent these restrictions by supplying special military products to Belgrade with civilian flights.
Thus, in 2019, Russia has received 10 permits from the Bulgarian civil authorities to fly over Bulgaria of its "civil aircraft transporting cargoes with special and military products with the final recipient the Republic of Serbia." In 2020, the number of permits, which was issued, is 5, and for the current year - 2. /BGNES