Modern active distribution networks possess significant potential to deliver ancillary services to transmission networks owing to the rising integration of renewable energy sources. This study explores the provision of primary frequency support from active distribution network to transmission network via price-based transactive control of microgrid inverters. The proposed method aims to achieve efficient coordination among microgrids, optimizing their utility, while also assisting the active distribution network in optimal primary frequency support provision to transmission network. The feasibility of this approach for real-time application is validated using a real-time simulator.