This publication presents the design of the Integrated Local Flexibility Market (LFM) developed within the Greek pilot of the EU-funded OPENTUNITY project. The pilot involves Hellenic Electricity Distribution Network Operator (HEDNO) as the Distribution System Operator (DSO), Independent Power Transmission Operator (IPTO) as the Transmission System Operator (TSO), and NODESTM as the Flexibility Market and Platform Operator. Flexibility Service Providers, despite actively participating in the LFM, are excluded from the study as the main concept surrounds TSO-DSO coordination. Within the Greek pilot, HEDNO will participate in the Integrated LFM to address local congestion, while IPTO will evaluate the procurement of flexibility for frequency control, and specifically for manual Frequency Restoration Reserve (mFRR). Resources will be connected to the distribution grid, employing NODESTM’ ShortFlexTM product. The market framework includes a dedicated rulebook, asset registration, and grid replication, facilitating efficient flexibility procurement. A key innovation is the coordination mechanism between TSO and DSO to avoid conflicting activations, tested through three distinct operational scenarios. These scenarios are evaluated based on resolution time and the proportion of successfully traded flexibility. The pilot demonstrates how integrated flexibility markets can enhance grid reliability and support scalable TSO–DSO cooperation.